Holley 4150 & 4160 Manual

CARBURETOR H A N D B O O K

SELECTION JU N IN G & REPAIR

MIKE URICH

H P B o o k s

METRIC CUSTOMARY-UNIT EQUIVALENTS

Multiply: by: to get: Multiply: by: to get:

LINEAR

inches X 25 4 - millimeters(mm) X 0 0 3 9 3 7 - inches

feet X 0 3048 - meters (m) X 3.281 - feet

miles X 1.6093 - kilom eters (km) X 0 6214 - miles

AREA

inches2 X 645.16 - m illim eters2(mm2) X 0 00155 -

VOLUME

o

inches

inches3 X 16387 - m illim ete rs^m m 3) X 0 000061 - inches3

inches3 X 0 01639 - liters (1) X 61 024 - inches3

gallons X 3 7854 - liters (1) X 0.2642 - gallons

feet3 X 28 317 - liters (1) X 0 03531 - feet3

feet3 X 0 0 2 8 3 2 - m e te rs^m 3) X 35 315 - fe e l3

flu id oz X 29 57 - m illilile rs (ml) X 0 03381 - flu id oz

MASS

ounces (av) X 28 35 - grams (g) X 0 0 3 5 2 7 - ounces (av)

pounds (av) X 0 4536 - kilogram s (kg) X 2.2046 - pounds (av)

tons (20001b) X 907.18 “ kilogram s (kg) X 0 001102 - tons (2000 lb)

FORCE

p o u n d s -f(a v ) X 4.448 - newtons (N) X 0.2248 - p o u n d s-K a v)

k ilo g ra m s -f X 9 807

newtons (N)

X 0 10197 - kilogram s—t

TEMPERATURE

Degrees C elsius (C) -

0 556 (F - 32)

Degree Fahrenheit (F) - (1 .8 0 +

” F -4 0

1 ll

*C -4 0

32

98 6

212

0 140 80 I 120 160 200

1 1 1 1 | 1 1 1 1 , 1 , 1 1 1 . 1 I I I I

1 1 1 ' I ' 1 ’ 1

20 0 20 40 6 0 80 100

240 280

I , I , I , |

H f ' 1

120 140

320

J

H

160 ° C

ACCELERATIC>N

feet/sec 2 X 0 3048 m eters/sec2(m /s2) X 3 281 - feet/sec2

ENERGY OR WORK (W att-second “ joule -n ew ton-m ete r)

foot-pounds X 1 3558 joules (J) X 0 7376 - foot-pounds

Btu X 1055 joules (J) X 0 000948 - Btu

FUEL ECONOMY A FUEL CONSUMPTION

m iles/gal X 0 42514 kilom eters/liter(km /l) X 2 3522 - miles/gal

Note: 235 2/(m i/gal) - lit e r s / 1 0 0 km

235 2 /(lite rs /100km) - m i/gal

PRESSURE OR STRESS

inches Hg (60F) X 3 3 7 7 kilopascals (kPa) X 0 2961 _ inches Hg

pounds/sq in X 6.895 kilopascals (kPa) X 0 145 - po unds/sq in

inchesHjO leOF) X 0 2 4 8 8 kilopascals (kPa) X 4 0193 - inches H^O

POWER

horsepower X 0 7 4 6 kilow atts (kW) X 1 34 - horsepower

TORQUE

pound-inches X 0 0115 kilogram -m eters (Kg-M) X 87 _ pound-inches

pound-feet X 0.138 kilogram meters (Kg-M) X 7 25 - pound-feet

VELOCITY

m iles/hour X 1 6093 kilom eters/hour(km /h) X 0 6214 m iles/hour

feet/sec X 0.3048 m eters/sec (m/s) X 3 281 - feet/sec

kilom eters/hr X 0 2 7 7 7 8 m eters/sec (m/s) X 3 600 - kilom eters/hr

Conversion Chart courtesy Ford Motor Company

HOLLEY* *1150 & 60

HANDBOOK

Introduction ....................................................................................... 2

1 Fuel-Inlet System ....................................................................... 6

2 Idle System .................................................................................. 12

3 Main Metering System ............................................................... 16

4 Power System .............................................................................. 22

5 Accelerator-Pump System ........................................................ 26

6 Secondary System ...................................................................... 32

7 Choke System ............................................................................ 38

8 Specific Models ........................................................................... 44

9 Carburetor Selection .................................................................. 52

10 Metering Blocks ........................................................................... 57

11 Repair and Adjustment ............................................................... 60

Index .................................................................................................. 80

Library of Congress Cataloging-in-Publication Data

Urich, Mike.

Holley carburetor handbook 4150 & 4160

Reprint. Originally published: Tucson : HP Books,

1980.

Cover title.

Title on spine: Holley 4150/60 carburetor handbook.

Includes index.

1. Automobiles— Motors— Carburetors. I. Title.

II. Title: Holley carburetor handbook 4150 and 4160.

III. Title: Holley 4150/60 carburetor handbook.

IV. Title: Holley four thousand one hundred fifty/sixty

handbook. V. Title: Holley carburetor handbook four

thousand one hundred fifty & four thousand one

hundred sixty. VI. Title: Holley carburetor handbook

four thousand one hundred and fifty & four thousand

one hundred and sixty.

TL212.U75 1987 629.2'533'0288 80-82385

ISBN 0-89586-047-3 (pbk.)

HPBooks are published by

The Berkley Publishing Group,

200 Madison Avenue, New York, New York 10016.

©1980 Price Stern Sloan, Inc.

Printed in the U.S.A.

20

NOTICE: To the best of the author’s knowledge, the information contained in this book is true and

complete as of the date of publication. However, due to normal variations in manufacture and other

factors, the recommendations on carburetor selection, installation, tuning, etc., are necessarily

made without guarantees of any kind on the part of the carburetor manufacturer, the author or the

publisher. Because design matters and methods of application are, and must be, subject to change,

and beyond the author's control, the carburetor manufacturer, the author and the publisher expressly

disclaim any and all liability whatever arising or alleged to arise, out of use of any Information contained

herein. Part's numbers and specifications will change and the availability of parts will change

as improvements continue to be made in Holley carburetors.

An independent publication — not published by or associated with Holley Carburetor Division, Colt

Industries Operating Corporation.

INTRODUCTION

For more than two decades

Holley brand carburetors have

enjoyed tremendous popularity

with people who purchase replacem

ent c a rb u re to rs : ra c e rs,

enthusiasts or almost anyone with

a carburetor need. Over this time

span, Models 4150 and 4160 have

been the stars of the line, attracting

by far the most attention.

One of the prime reasons for

this continued popularity has to be

the modular design concept, which

allows easy changes and modifications.

The carburetor is the first

and most common item the

enthusiast changes, and Holley

makes it easy with these models.

I have been closely involved

with these carburetors over the

years, and I’d like to share my

experience with you by taking you

through the carburetors system by

system, pointing out features,

available options and tips along the

way. I’ll talk about a few of the

more popular versions. In the last

section I’ll cover the teardown,

repair and adjustment of a typical

4150 carburetor.

Holley 4150 carburetors were

first introduced on Ford 312 CID

engines in 1957 and gained added

popularity on small- and big-block

2

Example of the modular concept. Removing 8 fuel-bowl screws gets you to the point

where most calibration changes are made. I know of no other carburetor with so many

modification possibilities—bowls, inlet valves, jets, pump shooters, power valves, pump

cams, choke configurations and many more as shown on these pages.

Secondary-metering systems. The 41 60 on the left shows the small metering plate held in

by clutch-head screws. The 4150 on the right has a metering block similar to the primary

side. In this particular example the power-valve passage is not machined—not true in all

cases.

3

Chevrolet engines in the 1960’s. A

lot of 4150 and 4160 carburetors

are still used today on governed

and non-governed trucks.

A great variety of 4150 and 4160

carburetors are currently offered,

ranging from 390 to 850 CFM.

Vacuum-secondary types are

available in various sizes to fit

almost any requirement. Mechanical-secondary

types with “doublepumper”

or twin acceleratorpumps

are available in 50 CFM

increments from 600 to 850 CFM.

4150 and 4160 carburetors are

so similiar you might not be able

to tell them apart unless you knew

what to look for. They are identical

in operation and—except for the

secondary metering block —their

construction is identical.

The 4150 has a secondary

metering block with the same

physical dimensions as the primary

metering block sandwiched between

the secondary fuel bowl and

Kit 34-6 converts 4160's to 4150 configuration with a metering block using replaceable

main jets. Longer bowl screws, metering block, gaskets and a longer fuel-transfer tube

are included. This kit is also used when converting a 4160 to use race-type center-hung

fuel bowls. Lead balls are included in the kit for closing the holes left when the balance

tube is removed.

4

the carburetor body. A secondary

metering plate with machined

orifices is screw-attached to the

body of 4160 carburetors. This

metering plate is simpler in construction

than a metering block. It

requires less drilling, no plugging

or tapping, and has no screw-in

main jets or power valve.

All current 4160 carburetors

have vacuum or diaphragm-operated

secondaries. None have

mechanical linkage or doublepumper

arrangement. Several

fuel-bowl types are used, depending

on user requirements.

4160 carburetors have been

used by American Motors,

Chevrolet, Chrysler and Ford as

original-equipment (OEM) carburetors.

They are just as highperformance

oriented as any of the

4150’s and can be converted to a

4150 with a kit.

Why the difference? The model

4160 offers high performance at a

lower cost. Also, the smaller

physical size of the 4160 allows fitting

two carburetors on a manifold

where this might otherwise be

impractical.

Quite a few 4160 carburetors are

offered, including a line of emission-oriented

600 CFM versions.

I’ll talk more about these later.

Conversion kit 34-6 is a must

for the individual who wants to

calibrate his 4160 carburetor for

optimum performance. The kit

includes a secondary metering

block, gaskets, longer bowl screws

and a longer transfer tube.

List 3310-1 features center-pivot fuel bowls and vacuum-operated secondaries.

5

1 FUEL-INLET SYSTEM

Schematic ot the inlet system. Here the float has not reached the desired level, so the

inlet valve is off its seat and admitting fuel to the bowl. Fuel flow will shut off when the

float rises to close the inlet valve.

6

Fuel enters the primary fuel

bowl through a screen or filter and

passes through the inlet valveand-seat

assembly into the fuel

bowl. The fuel bowl contains the

fuel-inlet fitting, inlet valve and

seat assembly and the float.Where

there is only one fuel inlet for the

carburetor, fuel reaches the secondary-bow

l valve-and-seat

through a transfer tube O-ring

sealed to each fuel bowl. In some

cases, an external inlet on the secondary

bowl must be separately

plumbed.

Referring to the schematic,

think of the float and inlet valve as

a scale balance with the hinge pin

as the pivot. Fuel pressure against

the inlet valve provides the opening

force while the buoyancy of the

float in the fuel provides the closing

force. This increases as fuel

rises on the float. Fuel level is a

result of the balance of opening

and closing forces.

Change this balance and you

change the fuel level. For instance,

increasing the inlet seat size or fuel

inlet pressure raises the fuel level,

so the float level should be

lowered to compensate. A rule of

thumb is that a fuel pressure

increase of 1 psi (pounds per

square inch) raises fuel level 1/32

inch.

The fuel bowl is a reservoir. The

level of fuel in the bowl must be

maintained at a specific value for

proper carburetor operation. This

level varies slightly from carburetor

to carburetor.

As fuel enters the bowl, the

float rises with fuel level and acts

to close the inlet valve.

All bowls are vented to the carburetor

air horn to maintain a constant

“ reference” pressure. This

keeps airflow variations—like a

dirty air filter —from upsetting the

mixture.

In some cases the bowl is also

vented to an outside canister at

idle and when the engine is turned

off. The canister stores fuel vapors

as a means of controlling evaporative

emissions. These vapors are

drawn into the engine and burned

when it is restarted.

There are two kinds of bowls,

depending on the float mounting.

One mounts the float at the end of

the bowl. These are called frontmounted,

even though the rear

bowl hinges the float at the rear.

The other kind —side-mounted—

mounts the float at the side of the

bowl.

All front-mounted float bowls

have a separate, external fuel inlet

and externally adjustable inlet

valve. Some have inlets machined

on both the right and left sides for

plumbing convenience. Bowls with

side-mounted floats come in both

external and internal adjustment

versions. Primary and secondary

bowls are connected by a balance

tube.

Generally speaking, frontmounted

float bowls are best for

circle track or road racing where

fuel movement is sidc-to-side.

Side-mounted float bowls are best

for drag racing, where the fuel

movement is fore-and-aft. Some

drag racers give up this advantage

to get the separate inlet feature of

7

Cutaway race-type bowl shows adjustable needle/seat assembly (1), adjusting nut (2),

and lock screw (3). Sintered-bronze filter (4)inlet has spring (5) to allow fuel bypass if

filter plugs up. Fuel-inlet nut (6) can be swapped with plug (7) on some race bowls to allow

plumbing to opposite side. Inside view shows half of float (8) and segment of mounting

bracket (9).

8

front-mounted float bowls.

Floats are constructed of brass

or closed-cell synthetic material.

Both have advantages and disadvantages.

Brass floats may be used with

any fuel but are more prone to

leak. They should never be used in

turbocharged applications that

blow through the carburetor

because they may collapse from

the added pressure. Synthetic

floats can withstand the pressure

from a blow-through turbocharger

application but should never be

used with any fuel other than

gasoline. They can also be molded

in unusual shapes.

Most floats have a spring acting

on them, either at the hinge pin or

underneath the body. Under

bumping or jouncing conditions

this spring helps the float control

fuel level.

Side-hung float In secondary fuel bowl shows float (1), adjustable needle/seat assembly

(2), adjusting nut (3), lock screw (4), plastic baffle to direct inlet fuel and contain froth

(5), float bumper spring (6), sight plug for fuel-level checking (7), and hole for transfer

tube which brings fuel to secondary bowl from inlet on primary bowl (8). When correctly

set up, half-round float Is adequate for all but the most severe cornering loads like those

generated in autocrossing, road racing or on an asphalt oval track.

9

Inlet valve-and-seat assemblies

are available in a variety of sizes

for the 4150/60 carburetors.

Externally adjustable inlet

valve-and-seat assemblies are

available with steel valve tips in

seat sizes from 0.097 to 0.120-inch

diameter and Viton tips from

0.097 to 0.110-inch diameter. The

Viton tip has superior sealing

characteristics to minimize fuellevel

creep. Steel inlets should be

used with fuels other than

gasoline.

Internally adjustable valve-andseat

assemblies are available with

Viton tips only, in sizes from 0.082

to 0.110 inch. Accompanying

charts show flow capabilities of

various inlet-seat sizes.

Increasing inlet-seat size is a

good-news/bad-news story. The

good news is: Fuel flow rate will

increase. The bad news is: Fuel

handling control will be sacrificed.

Don’t install a larger seat unless

your engine really needs the extra

flow. If you install a larger seat and

get no measurable performance

improvement, reinstall the seat

size you started with.

Some inlets contain a sinteredmetal

filter. This filter is not

intended to do the job all by itself

and should be used in conjunction

with an in line filter between the

fuel pump and carburetor. Some

racers remove this sintered filter

to cut down restriction. In either

case don’t forget to use an inline

filter.

Round-hole needle/seat assembly is used

for low-flow applications. “Picture-window"

assemblies are common where higher

flow is required. O-ring seals inlet side

from fuel bowl. Threaded portion provides

for fuel-level adjustment when used with

adjusting nut and locking screw.

Typical non-adjustable inlet assembly. The

number is the seat diameter (0.110”). The

spring clip gives positive opening force to

the float hinge. Non-adjustable simply

means that the valve itself can’t be

adjusted. Fuel level is adjusted by bending

the float tab.

10

Actual measured gasoline flow

through wide open, 0,110-inch

diameter window-type Inlet valve

assembly. Float held at bottom of

bowl.

FUEL FLOW vs. FUEL PRESSURE FOR VARIO US SIZE

NEEDLES & SEATS

Dia. o f Needle

Seat

Type

Fuel F lo w

@ 2 P.S.I

Ibs./hr.

Fuel Flow

@ 4 P.S.I.

Ibs./hr.

Fuel Flow

@ 6 P.S.I.

Ibs./hr.

0 .0 8 2 " Holes 106 153 204

0 .0 9 7 " Holes 121 174 225

0 .1 0 1 " Holes 138 194 254

0 .1 1 0 " Holes 153 230 275

0 .1 1 0 " W indows 160 232 295

0.120 W indows 167 236 305

N O T E :

Checked w ith needle & seat assembly installed w ith flo a t held a t b o tto m o f bowl.

11

2 IDLE SYSTEM

Mixture adjusting screw controls fuel flow at idle. Air bleeds are located in the air horn.

12

The idle system serves several

purposes. It provides a richer mixture

at idle, provides idle-mixture

adjustments to compensate for

engine and tuning changes and

supplies fuel during the transition

from idle to part-throttle or cruise

conditions.

At idle, fuel Hows from the fuel

bowl through the main jet and into

the main well. From the main

well, fuel flows through an idlefeed

restriction into the idle well,

up the idle well and mixes with air

from the idle-air bleed. The idlefeed

restriction can also be at the

top of the idle well, or at the bottom

of a tube pressed into the

well.

The fuel then proceeds down

another passage. At the bottom of

the passage, the idle fuel branches.

One leg goes to a transfer slot

above the throttle. The other goes

below the throttle plate, past the

adjustment needle, to a hole in the

throttle bore. Most of the fuel is

Holes in throttle plates (solid arrows) keep

correct relationship of throttles to the idletransfer

slots (outline arrows). Note that

they are on the same side of the throttle

shaft as the transfer slots.

supplied through this hole at curb

idle—engine warmed up and idlcspeed

adjustment screw on stop.

An idle system is provided for

each barrel, but in most cases only

the primary systems are adjustable.

Other than this adjustment

feature, primary and secondary

idle systems are essentially identical.

Some Holley carburetors have a

“ reverse” idle adjustment. Screws

turned in to richen and out to lean

Idle System

Idle air bleed

Idle feed

restriction

Idle well

Idle

transfer

passage

transler

slot

discharge

hole

idle adjusting needle

Main jet

13

"R everse” Idle System

Primary

metering

Reverse-idle-adjustment needle controls idle air rather than idle fuel. Mixture is leaned

when the needle is backed out and richened when adjusted in.

Carburetors equipped with the "reverse”

idle system have a label on the metering

block. The adjustment is leaned by turning

the adjustment screw counter-clockwise

(admitting more air, as shown in drawing

above.)

14

the mixture—exactly opposite to

what has always been done in the

past. Labels indicate the adjustment

change.

This difference came about as

part of a development program to

improve idling with mixtures lean

enough to meet emissions requirements.

The “ reverse” system is shown

in the accompanying drawing.

Note the adjustable second air

bleed in this new idle circuit. The

mixture screw, which once varied

the mixture outlet area, now

varies inlet air area through a

second air bleed. This air bleed is

connected to the air section just

below the venturi throat.

In most cases it shouldn't be

necessary to alter the idle feed or

bleed restrictions, but if you have

to, work on the feed— fuel flow;

not the bleed— air flow. Remember,

these restrictions are pressed

in and are not easily available.

TUNING TIP

Maybe you’ve installed a performance

camshaft and the engine

refuses to idle at normal speeds.

The idle-mixture screw does little

or nothing.

Try to get the engine to idle,

regardless of the speed or

quality of the idle. Without

changing any setting, take off

the carburetor and see where

the throttle plate is in relation to

the idle transfer slots or holes. If

they are exposed there is a simple

fix.

What’s happened is that the

cam’s increased overlap has

caused a loss of manifold

vacuum at idle. The throttle must

HOT IDLE COMPENSATOR

Certain models of 4150/60 carburetors

were equipped with a

Hot Idle Compensator (HIC).

This device was designed to

provide an additional air bleed at

idle to combat excessive richness

brought on by fuel evaporation

during extended idle

periods.

The device consists of a therbe

opened farther to get adequate

mixture flow, but this

increased throttle angle exposes

the transfer slot. Idle mixture

then flows through the transfer

slot; the engine runs excessively

rich and no longer responds to

the idle-mixture screw.

H ere's how to solve the

problem. Drill a small hole, about

3/32- or 1/8-inch diameter, in

each primary throttle plate on

the same side as the idle-circuit.

Some air will pass through the

holes, allowing you to close the

throttle plate to somewhere near

its original position. The idle

adjustablity will return.

m o sta tica lly contro lle d fla t

spring, a valve and an air bleed.

When a certain underhood temperature

was reached, the valve

would lift off its seat to allow

more air into the idle circuit.

This valve was seldom needed

in the past few years due to the

leaner idle mixtures and fuel

bowls vented to the canister.

15

3 MAIN METERING SYSTEM

Main-system fuel flow begins at the float bowl. Fuel is routed through the main jet into the

main well where the fuel is pre-mlxed with air. This air/fuel mixture is then routed to the

booster venturi via the discharge nozzle.

16

At cruising speeds, fuel flows

from the fuel bowl, through the

main jet into the bottom of the

main well. Fuel then moves up the

well and mixes with air from the

main air-bleed holes in the side of

the well. These air-bleed holes are

supplied with filtered air from

openings in the carburetor air

inlet, called main air-bleed restrictions.

The mixture of fuel and air

moves up the main well to the discharge

nozzle located in the

booster venturi.

Main Jets —These metering

orifices control fuel flow into the

metering system. They are rated in

flow capacity—cubic centimeters

per minute—and are changeable

for tuning purposes.

There is a basic misconception

about jets—that size alone determines

their flow characteristics.

The shape of the jet entry and

exit—as well as the finish—also

affects flow. Holley checks each jet

on a flow tester and grades it

according to flow. This flow rate is

compared to a master chart and a

number is stamped on the jet to

indicate its flow.

Drilling out jets to increase flow

is never recommended because

this destroys the entry and exit

features to a certain degree, and

may introduce a swirl pattern,

even if the drill is held in a pin vise

and turned by hand. You cannot

be sure of the flow characteristics

of a jet that you modify by drilling—unless

you get that jet back

on a flow machine to compare it

with a standard jet.

17

MAIN-JET FLOW RATING

Tolerance range used for each

size explains why a 66 jet may

not seem to give a richer mixture

than a 65. If the 65 is on the

“ rich” side of its allowable

tolerance and the 66 is on its

"lean" side tolerance limit, the

two jets may flow very close to

the same amount of fuel.

There is a 3% flow range within

a jet size, and about 4.5%

difference in flow between

average jets in the two sizes.

Tolerance for a 65 ranges from

351.5 to 362.0 cubic centimeters

per m inute at a specified

pressure with a given test fuel.

66 ranges from 368.5 to 379.5

cc’s. Standard jets are available

as 22BP—40-XX, where XX is

the size.

In 1975 Holley developed a

close-limit series of main jets in

the standard size range of 30 to

74. This series was developed

so flow could be more closely

tailored to fit within emission

requirements. These jets use the

first two numbers to indicate

flow range, such as 65 or 66, and

a third number to indicate

whether the jet flows toward the

lean side (651) in the middle

(652), or rich (653).

In this series, there can only

be a 1.5% difference in flow between

two jets with the same

flow marking, as opposed to a

variation of as much as 3% in the

old two-digit numbering system.

The new jet series has the same

brass or aluminum color as was

previously used.

Holley offers the close-limit

jets in the mean sizes only, that

is, 652, 662, etc. You may have a

carburetor with a 551 or a 563 in

it, but these jets are only available

in the assembly plant where

the carburetor is made and flow

checked. Close-limit jets offer a

good way to accomplish fine

tuning, provided you can use

jets ranging from 35 to 74 (352

through 742). Order these jets

as 22BP-120-XX2. Consult the

currect Holley Performance

Parts Catalog for available sizes.

5 0 3 5 0 2 501 5 0

M M

These main jets all look alike except for the

markings. The 50 is the standard jet. 501,

502 and 503 are a close-limit series with

only 1.5% flow range difference (maximum)

between any jet with the same marking.

Two-digit (50) series jets had 3% possible

variation between any two jets with the

same marking.

MAIN AIR BLEED

Air bleeds emulsify the fuel —

mix fuel with air—to prepare it for

atomization and to lower the effective

viscosity of the fuel to

encourage earlier feeding of the

main system. A larger air bleed

leans the mixture and a smaller

one richens it.

The size also affects the nozzle

starting point— the engine speed

the nozzle starts to flow fuel. The

larger bleed delays the starling

point to a higher RPM. For this

18

Vacuum Trends: Throttled & Wide-

Open Throttle

Arrows (above) indicate the bleeds. The

outside ones are the idle air bleeds and the

two on the inside are main air bleeds. In

almost all cases idle bleeds are larger, as

seen here.

Typical vacuum drops inside a carburetor.

Slight vacuum at inlet represents drop

across the air cleaner. Gage at large venturi

throat shows higher vacuum because

air is still at relatively high velocity.

Vacuum returns almost to the inlet value

just before the throttle plate. Throttled carburetor

shows very high manifold vacuum

because a large pressure drop occurs

across the partially-opened throttle. Wideopen

carburetor’s low manifold vacuum

indicates a heavy-load/dense-charge

situation.

In both cases, the highest carburetor

vacuum is at the boost-venturi throat. The

signal to the main system is picked up here.

Wide-open throttle

High RPM

19

reason, I recommend that the

tuner not use bleeds to richen or

lean the mixture. Besides, the

bleeds are pressed in rather than

screwed in, so you’ll lose the press

fit after the first or second change.

For main-system recalibration,

main jets are the only way to go—

that’s why they are changeable.

Model 4150 and 4160 carburetors

are equipped with built-in

fixed-dimension air bleeds. A flat

surface in the air horn is typically

used for mounting these bleeds so

they will see total pressure and will

not be affected by air-flow variations.

Venturis, Boost Venturis and

Nozzles—The venturi is the controlling

sensor for the main

system. It also determines carburetor

air-flow capacity. As

velocity increases through the

v e n tu ri, absolute pressure

decreases (or the vacuum

increases if you prefer). When the

pressure drops low enough to lift

the fuel to the spill-over point,

main-system flow begins. The

greater the air velocity, the greater

the pressure drop and the greater

the fuel flow.

The boost venturi is a signal

amplifier located within the main

venturi. The fuel-discharge nozzle

is inside the boost venturi. As a

venturi within a venturi, the boost

venturi “sees” a lower absolute

pressure than the main venturi. To

increase this effect, the boost venturi’s

discharge is located at the

lowest pressure point in the main

venturi. This means the placement

of the boost venturi in the throat

Typical boosters. Most are spun-in, but

over the years there have been some cast

integrally with the main body. The one on

the left has a bell-bottom to restrict flow.

Center one is the most common. One at the

right has a slightly downward discharge

channel.

of the main venturi is extremely

important and should not be

changed.

A small venturi provides high

velocities, giving strong metering

signals and good atomization,

vaporization and mixing. The large

venturi gives reduced metering

signals and less effective atomization

at low engine speeds, but is

less restrictive to air flow, increasing

the engine’s power potential.

That’s why carburetor size is a

compromise.

20

ANNULAR DISCHARGE BOOSTERS

In 1980 Holley introduced

three new 4150 double-pumpers

utilizing a booster concept

known for some time but never

before used in performance carburetors.

The concept is annular

discharge. A typical installation

is shown in the above photo.

Note the different appearance

from other boosters shown in the

book. These carburetors have no

choke m echanism and are

intended strictly for competition

in single or dual carburetor

applications. Numbers are 0-

9379, 0-9380 and 0-9381 With

capacities of 750, 850 and 830

CFM respectively.

The reason for the improvement

is the higher air velocity

close to the venturi surface

where the discharge holes are

located. This increases the

metering signal and gets the

main system flowing at lower air

flows. This reduces dependence

on accelerator pumps to avoid

hesitation or bogs. This higher

signal, together with the equally

spaced, radial location of the

d is c h a rg e h oles im proves

atomization and cylinder-tocylinder

distribution. The higher

signal reduces main jet requirements

4 to 5 sizes.

This photo shows the twopiece

construction of the new

boosters. The top section, containing

the annular track and

discharge holes, is pressed into

the larger ring section. Larger

section contains the fuel discharge

channel from the main

well. The assembly is spun into

place by the same means as

conventional boosters.

21

4 POWER SYSTEM

Additional fuel is supplied by the power system under high-load conditions as the powervalve

spring overcomes low manifold vacuum.

22

At part throttle or cruise conditions,

the object is to conserve

fuel, so excess air is supplied to

consume as much of the fuel as

possible. The result is good fuel

economy and low exhaust emissions.

Typical fuel/air ratios for

economy are about 0.06 to 1 (16.7

to 1 air/fuel ratio).

At high-load conditions, the

object is maximum power, so we

want to consume all the air. This is

accomplished by supplying a little

excess fuel. Typical fuel/air ratios

for power are 0.07 or 0.08 to 1

(14.3 to 1 or 12.5 to 1 air/fuel

ratios).

During high-speed or high-load

operation when manifold vacuum

is low (n ear a tm o sp h eric

pressure), the carburetor automatically

provides this added fuel

for power operation.

A vacuum passage in the throttle

body transmits manifold

vacuum to a chamber in the main

body. When manifold vacuum

drops, a spring opens a power

valve in this chamber to admit

extra fuel. This fuel flows through

the power valve, through the

power-valve channel restriction

and into the main well. There it

joins the fuel flow in the main

metering system to enrich the

mixture.

When engine power demands

are reduced, manifold vacuum

increases and is applied to a

diaphragm in the power valve. The

power-valve-spring tension is

overcome and the valve is closed,

stopping the extra fuel flow.

Vacuum also holds this valve

O O

Cast slots in power valve at right increase

flow and cross-sectional strength. This

valve is stronger than the drilled type and

less likely to break off during installation or

removal. It is Inter-changeable with ail

older units, but gasket 8R-1597, with no

protrusions on the inside diameter, must be

used. The valve is offered in two sizes:

25R-591 -A for all power-valve-channel

restrictions up to 0.090 inch; 25R-595-A

for rare calibrations using larger PVCR's.

23

REMOVAL OF POWER VALVES

The only reason for removing the

power valve is when the induction

system is so restrictive that

manifold vacuum at wide-open

throttle gets above the rating of

the power valve. In this case the

valve will close, leaning the mixture.

The correct solution is to

use a higher rated valve. If you

do remove the power valve you

must jet up 6 to 8 main-jet sizes

to compensate.

Staged power valve. The number does not

designate the opening vacuum point in this

case. It is merely a part number.

closed at idle and normal load conditions.

Some 4150 carburetors have

power valves in both the primary

and secondary circuits, but most

have them only in the primary.

There is no power valve in the secondary

side of a 4160.

The power valve is simply a

“switch" that opens at a predetermined

manifold vacuum,

measured in inches of mercury

(Hg). It does not meter the fuel.

Metering is accomplished by the

pressed-in power-valve channel

restrictions (PVCR). The one

exception to this is the staged

power valve.

Staged valves are designed to

open partially at intermediate

manifold vacuum, say 10 or 12

inches lig. In this case the valve

actually meters, giving a slight

enrichment. At lower manifold

vacuum, about 4 or 5 inches Hg

the valve opens completely,

switching the metering function

back to the power-valve channel

restrictions. This valve tailors

fuel/air ratios for optimum

exhaust em issions and fuel

economy. There is a slight enrichment

in the intermediate range.

Full enrichment is delayed as late

as possible. These valves are easy

to recognize as seen in the accompanying

photograph.

Power valves are easily removed

and interchanged. The rating is

stamped on one of the hex flats. A

60 number means the valve opens

at 6.0 inches Hg, a 45 valve opens

at 4.5 inches Hg, etc.

24

TWO-STAGE POWER VALVES

Two-stage power valves were

developed to match fuel delivery

more closely to engine demand

to optimize driveablility, fuel

economy and exhaust emissions.

In addition to the driveability

improvements, fuel

economy increases were noted

on certain applications.

The reason for the fuel

economy increase is quite logical.

Under a load, such as

accelerating or climbing a hill,

manifold vacuum decreases as

more air is admitted to make

needed power. To make more

power, more fuel is needed.

With a single-stage power

valve, a full-power charge of fuel

is admitted to the air stream

when manifold vacuum drops

below a pre-determined level

(usually 6-8 in. Hg). Under many

circumstances, this full power

charge is not needed for moderate

acceleration and excess fuel

is used. This is when a twostage

power valve may provide a

fuel economy increase.

As additional air is admitted to

the engine and manifold vacuum

begins to drop, the first stage

opens and meters a partial

charge of fuel. This often provides

the needed power without

wasting the extra fuel needed for

full power operation.

If the vehicle load requires full

power, manifold vacuum continues

to drop, the second stage

opens and full power enrichment

is metered by the PVCR.

There is no way to guarantee a

fuel economy increase with twostage

power valves for all

applications, but an increase

will probably be realized if the

power valve is applied according

to the following guidelines:

1. The vehicle weight/engine

displacement ratio is 14:1 or

greater. This should also include

the weight of any loads the vehicle

normally carries.

2. The vehicle is not raced,

even occasionally.

3. Power-Valve Channel

Restrictions are less than .060” .

A number of 4150/60 carburetors,

including the 600 CFM List

6619 (below) and 6909, are

equipped with two-stage power

valves. Kits are available to convert

the older carburetors equipped

with single-stage power

valves to two-stage valves.

These restrictions should be

followed closely. Misapplication

of two-stage power valves can

result in a decrease in fuel

economy, so you could lose on

both the price of the valve and

excess fuel consumption.

Also, the List 3310 and the

conventional double-pumper

line require high-capacity power

valves. The limited flow of the

two-stage power valve can

result in excessive leanness and

engine damage under extended

acceleration.

25

5 ACCELERATOR-PUMP SYSTEM

Diaphragm-type accelerator pump. Fuel is drawn into the pump from the float bowl past

the check ball. When the accelerator linkage actuates the pump arm, the check ball

closes. Fuel is forced up through the discharge passage in the metering block, then past

the discharge check valve and out the nozzle.

26

The accelerator pump has two

functions:

1. To make up for the lag in fuel

delivery when the throttle is

opened and more air rushes in.

2. To make up for fuel condensing

onto the manifold surfaces when

the throttle is opened suddenly at

low engine speeds.

Because air is lighter —has less

mass—than fuel, airflow responds

much more rapidly than fuel flow

to changes in throttle setting.

Whenever the throttle is opened,

the engine instantly receives more

air through the larger throttle

opening. But fuel How in the main

system doesn't respond as quickly

to match this increased air flow.

The accelerator pump mechanically

injects the additional fuel

needed until the main metering

system restores the correct fuel/air

ratio.

The lag in fuel flow is compounded

when the throttle is

opened suddenly at low RPM

because a large, instantaneous

drop in manifold vacuum occurs.

A high manifold vacuum tends

to keep the m ixture well

vaporized. As manifold vacuum

drops, fuel drops out of the fuel/

air mixture, condensing on the

intake-manifold surfaces. Thus,

the mixture instantly leans out,

and unless more fuel is immediately

added, the engine hesitates

or stumbles.

This additional fuel is especially

important with big-port heads and

manifolds, and manifolds with

large plenums (volume below the

carburetor) because there is less

Accelerator-pump discharge nozzles are

targeted so the pump shot "breaks" on the

booster venturi. Photo taken with carburetor

on Holley air box shows how shot Is

pulled toward lower edge ot booster venturi

by air streaming into the carburetor.

Bubbly fuel flow from main discharge

nozzle issuing from tail of booster indicates

air is already mixing with the fuel.

air/fuel velocity and these have

more surface area where fuel can

condense.

To counteract this low-flow,

low-vacuum period, the accelerator

pump injects (shoots) fuel into

the throttle bore the instant the

throttle is opened. This “ shot"

must be carefully metered because

the low mixture velocity will cause

much of the fuel to drop out

before it reaches the cylinders.

Duration of the shot must also be

carefully engineered to provide a

“cover-up” long enough to allow

main-system How to be established.

27

This function —mechanical

injection —is most important when

the carburetor is somewhat higher

in capacity than ideal for the

application or with a doublepumper

type carburetor using

mechanical secondaries.

The accelerator pump on the

4150/60 is diaphragm operated

and located in the bottom of the

primary fuel bowl. Doublepumper

carburetors have accelerator

pumps in both the primary and

secondary fuel bowls.

When the throttle linkage actuates

the pump lever, pressure

forces the pump-inlet check valve

onto its seat. This prevents fuel

from flowing back into the fuel

bowl. Fuel flows from the pump

through a long diagonal passage in

the metering block to the main

body. There the fuel pressure

raises a discharge check needle off

its seat and fuel sprays into the

venturi from the discharge nozzle.

As pressure drops in the pump

passages, the pump-discharge

check needle reseats to prevent air

from entering the pump chamber

as it refills. As the throttle closes,

the pump linkage moves towards

its original position and a spring

forces the pump diaphragm down.

The pump-inlet valve opens and

the pump refills with fuel. This

check needle also prevents airflow

past the discharge nozzles from

pulling fuel out of the pump

passages.

Pump movement is controlled

by a plastic cam on the throttle

lever. This cam acts on the

accelerator-pump lever through an

intermediate lever. The cam determines

the displacement or volume

capacity of the pump measured in

cubic centimeters per 10 strokes. The

TUNING TIP

If, upon opening the throttle

completely, the vehicle accelerates

well initially and then bogs

(hesitates), you'll need to extend

the shot by installing a smaller

shooter. You may also want to go

to a greater capacity cam. If the

vehicle bogs initially and then

moves well, you need a larger

shooter to get more initial fuel.

Be sure to follow the adjustment

procedures described later in

this book.

Accelerator-pump discharge nozzles or

“shooters” are marked with numbers

indicating diameter of holes in thousandths

of an inch. The ones at the left have discharge

tubes to better direct the flow.

28

Accelerator-P um p System

Discharge

nozzle

High-capacity (50cc per 10 strokes) accelerator-pump kit 20-11 is often added when

large secondaries are being opened quickly or where the engine has a wild camshaft. They

are also helpful when the carburetor is a long way from the intake ports. The pump is often

called a “Reo" pump because similar ones were used on Reo trucks. Installation may

require raising carburetor with a 1/4-inch-thick aluminum spacer so pump lever will clear

the manifold.

29

ACCELERATOR PUMP CAPACITY WITH D IFFER EN T CAMS

D EG R EES O F T H R O T T L E O PENING

10 20 30 40

-t--------- H---------- 1---------- *-

Cam in p o sitio n 1

0 10 20 30

Cam in p o sitio n 2

40

- I -

W H IT E

19.5cc

O R A N G E

19cc

O R A N G E

24.5cc

^ G REEN

24cc

G R EEN

30cc

This graph was made from tests of the various cams run with a high-capacity pump (50cc

per 10 strokes maximum), clearance of 0.015 inch on the pump lever at WOT, and constant

idle air flow. Capacities are in cc's per 10 strokes.

30

cam profile determines how this

volume is spread out over the

angle of travel.

Cams are easily changed to

tailor the pump shot. Capacities of

the various cams are shown on the

accompanying chart. Additionally,

each cam can be installed in two

positions with position 1giving the

lower capacity. Holley offers a

selection of five cams listed as Part

No. 20-12. The drag racer may

want to alter his cam by rotating it

so full cam movement is available

beginning at the throttle opening

required for staging RPM. This

may require new holes in the cam.

Pump-discharge nozzles or

“shooters” determine the rare of

pump discharge. The smaller the

orifice, the longer the shot will be

spread out. Orifice size is stamped

on the removable pump nozzle.

For instance, “ 25” means the

orifice diameter is 0.025 inch. Replacement

nozzles are available in

sizes from 0.026 to 0.037 inches

with or without discharge tubes.

A few carburetors are originally

equipped with a high-capacity

accelerator pump. This pump is

included in kit Part No. 20-11.

Because the high-capacity pump

has more travel, its housing is

larger, so be sure there is enough

clearance to the manifold. The carburetor

may have to be spaced up

or the intake manifold ground

away slightly to allow a full stroke

on the pump.

4150s with mechanical secondaries have two accelerator pumps.

31

6 SECONDARYSYSTEM

Diaphragm-operated secondary throttle. Initial opening Is caused by signal from primary

venturi. As secondary throttle starts opening, vacuum from primary venturi is augmented

by an increasing signal from secondary venturi.

Opening rate of secondary is controlled by spring behind diaphragm and size of restriction

through which vacuum is applied. Closing primary throttle closes secondary by

mechanical override linkage. As signal from the venturi ports “dies" (pressure moves toward

atmospheric) check ball blows off seat to remove vacuum from diaphragm chamber.

32

Why a secondary system? Well,

it’s a way of “ having your cake

and eating it too” —all it costs is

money. A staged carburetor has a

reasonably sized primary side to

take advantage of the good things

brought about by high venturi

velocities—strong metering signals

plus good mixing, atomization

and vaporization. At the same

time, having a second carburetor

as a backup, called the secondary

side, gives added flow capacity to

allow the engine to reach its full

power potential.

The secondary side of the carburetor

has a fuel-inlet system, an

idle system, a main-metering

system and—in the case of doublepumpers—an

accelerator-pump

system. Some secondary systems

may also have a power valve. In

nearly all instances, these systems

operate exactly like those on the

primary side.

Secondary systems are operated

either by a vacuum diaphragm or

by mechanical linkage.

With vacuum-operated secondaries,

opening signal comes from

the primary main venturi.

Vacuum from the venturi is

routed through the main body to a

diaphragm connected to the secondary

throttle lever. A spring inside

the diaphragm housing presses on

the diaphragm to keep the

secondaries closed.

As airflow through the primary

venturi increases, so does the

vacuum acting on the diaphragm.

Eventually vacuum overcomes

spring pressure and the diaphragm

“ pulls” the secondaries open.

Diaphragm-operated secondary opens as

the engine needs added airflow. This type

of secondary operation is very "forgiving”

in terms of size selection. A too-large carburetor

(in airflow capacity) can often be

used without spoiling low-end performance

and drivability. Arrow indicates secondarythrottle

stop.

On most models the opening

rate is also controlled by a restriction

in the vacuum passage from

the primary venturi. Certain

models have an additional passage

and bleed in the secondary venturi

to further control the opening rate.

When the primary throttle

closes, a check ball in the diaphragm

housing “dumps” the

vacuum in the housing and the

secondary throttle closes. On this

type of carburetor, the only mechanical

link between the primary

and secondary throttle levers is a

safety link that pulls the secondaries

toward the closed position as

the primary lever closes.

Several items affect secondary

opening:

1. Primary venturi size.

2. Diaphragm size.

3. Primary pick up and secondary

bleed relationship.

4. Spring rate and preload.

33

Exploded view of diaphragm used to operate secondary throttles. When tuning secondary

throttles for a different opening point, the spring is only element which should be varied.

Air cleaners also affect the opening

point, because the diaphragm

is vented to the atmosphere and it

“sees” the vacuum drop across

the air cleaner. This drop is added

to the induced vacuum in the venturi.

The greater the cleaner restriction,

the earlier the diaphragm

will operate.

The thing to remember is the

system allows you to program the

primary/secondary-opening relationship.

The object is to actuate

the secondaries as early as possible

for maximum engine output, but

not so early as to lose the signal

and main-system flow in the primary

venturi with a resultant sag

or bog. Once programmed, the

carburetor will always behave the

same. Performance programming

can be accomplished either on a

dynamometer or at the track.

With vacuum-actuated secondaries,

don’t use a thick stack of gaskets

between the carburetor and

manifold. This can distort the

throttle body and bind the secondary

shaft. Remember, you are

dealing with a delicate balance of

forces in the system so any change

of forces changes the opening

characteristics.

The diaphragm-secondary carburetor

is less sensitive to engine

size and vehicle variations, so

picking the size is not as critical as

with mechanical secondaries.

Some people object to the feel of

controlled, or vacuum secondaries

because the driver opens only the

primaries, the secondaries are

opened by engine demand.

Mechanical-secondary operation

is quite simple. When the primary

throttle reaches a given point—

usually about 40 degrees—a link

acts on the secondary lever. The

secondaries open faster, so primary

and secondary throttle plates

reach wide-open simultaneously.

Most mechanical-secondary carburetors

are 4150’s and have an

accelerator-pump on both the pri-

34

SE C O N D A R Y T H R O T T L E O P E R A TIO N RANGES

Diaphragm Secondary Springs From 85BP-3185 Used in M odel 4 150, L ist 3310-1 Carburetor

3 5 0 C ID Engt ie 4 0 2 C ID Engine

Spring Color R P M to Open RPM at Full O pen R P M to Open R P M at Full Open

Y e llo w (s h o rt spring) 1620 5 6 8 0 1410 4 9 6 0

Y e llo w 1635 5 7 5 0 1420 5020

P urple 1915 6 9 5 0 1680 6 0 5 0

P la in (S td . S pring) 2 2 4 0 8 1 6 0 1960 7130

B ro w n 2 7 1 0 8 7 5 0 2 3 8 0 7 6 5 0

Black 2 7 2 0 N o t fu iiv open at

m a x im u m a«r flo w

2 3 9 0 N o t fu lly open at

m a x im u m a ir flo w

N O T E : A ll d a ta taken w ith o u t a ir cleaner A n a ir clean® ' w o u ld cause e a rlie r o p e n in g m a ll cases. V alues

s u b ie ct to change d u e to cle a n e r re strictio n s.

Formula CFM - wne" V ‘ Volumal.ic Ell - 9

Chart and table clearly indicate relationship of secondary diaphragm springs and opening

points for two popular engine displacements. The slope of the lines indicates the secondary

opening rate. A shallow slope opens more quickly.

Note how displacement affects opening point. A larger engine opens secondaries earlier.

The springs toward the bottom of the graph allow sooner secondary opening. The yellow

spring is the fastest-opening spring supplied in the kit 20-13. The black spring delays

secondary opening the longest and opens them at the slowest rate. The bottom spring

(white) is a clear or “plain” steel spring.

35

(Above) Early style double-pumper mechanical linkage. Action is through the cam-driven

pin to an intermediate lever and then to the secondary lever.

Double-pumper mechanism introduced in 1976, Action is direct with fewer parts. Note

the slot in the secondary lever that takes up link travel during early primary opening and

delays the secondary opening. The secondary lever moves faster once it starts due to a

smaller radius.

36

mary and secondary sides, hence

the name “ double-pumpers.”

Mechanical secondaries let the

driver control secondary opening.

Also, a lower restriction offers a

torque gain in the middle speed

range of wide-open throttle.

When the throttle is “ punched”

wide open, air flows through all

four barrels—giving a lower

velocity in the primaries and a

lower signal. In most cases, the

added pump makes up for this,

but caution must be used in

matching carburetor size to the

vehicle and engine. That’s why

double-pumpers come in 50-CFM

increments from 600 to 850 CFM.

People have been known to convert

diaphragm secondaries to

mechanical by installing a

screw in the secondary lever

and disconnecting the diaphragm.

The result is usually

CAUTION

disastrous—a big bog when the

throttle is opened suddenly.

Throttle jamming can also

result. Never do this. If you want

mechanical secondaries, use a

double-pumper.

In 1978 two competition Model 4150 double pumpers were introduced, R-8156 and R-

81 62. They flow 750 and 850 CFM respectively. Some racers prefer the old-style throttle

linkage, so its’s used on these two. Adjustable idle on the secondary side is another

response to racers’ requests. These carburetors have no choke.

37

7 CHOKE SYSTEM

Therm ostatic coll

(bimetal)

Warm air

trom

choke stove

Warm

nlr in

Qualifying

linkage

Vacuum applied

to diaphragm

"k ic k s " choke

partially open

once engine

starts

Idle system

fuel (lowing

M anifold vacuum

passage

Immediately after engine startup, choke plate is partially opened, or "qualified," with this

diaphragm and linkage .

38

The choke must perform

several functions. First, it must

provide an extremely rich mixture

to start a cold engine. Closing the

choke plate tight in the air horn

causes a strong signal at the discharge

nozzle. This gives the

engine an extremely rich mixture.

A much leaner mixture is

required once the engine has

started, but still quite a bit richer

than normal. As the engine gets

warmer the choke gradually

opens —leaning the mixture to a

normal level.

Extra power is needed to idle a

cold engine, so a fast-idle cam is

mounted to the choke-control

shaft. The throttle stops against

this cam during choking to give a

greater throttle angle and a faster

idle to aid atomization.

Model 4150 and 4160 carburetors

have two basic types of

chokes—manual and automatic.

With the manual choke, most of

the above functions are performed

by the driver through a control

cable that operates a choke lever.

This lever operates the choke plate

through a rod. The choke plate is

offset on its shaft and springloaded

toward the closed position

so the plate opens as airflow

increases —providing a leaning

effect.

Automatic chokes take two distinct

forms— remote and integral.

Both types use a bimetallic spring

as an engine heat sensor. This

spring is made of two metals with

different thermal expansion rates.

Because the metals are bonded

together, the spring winds and

unwinds with temperature change.

With the remote choke, the

bimetal is located in a pocket in the

exhaust-heat crossover in the

intake manifold. It operates the

intermediate choke lever through

a rod.

The integral choke has the

bimetal spring in a housing

attached to the main body. The

bimetal spring acts directly on the

intermediate lever. Engine heat

from either the crossover or the

exhaust manifold is delivered to

the housing through an insulated

tube. Air Hows through the choke

housing into a passage to manifold

vacuum. This passage has a

restriction to control flow rate.

Manual choke (arrows indicate cablehousing

clamp and lever clamp for cable).

39

From the intermediate lever on,

operation is the same in both

cases. The intermediate lever

works the choke plate lever

through a rod.

Some remote chokes have an

electric heater to assist the choke

until the engine reaches a given

temperature. Electric heating units

are also used in some integral

chokes to perform the total heating

function in place of hot air.

Stringing a wire is a lot easier than

plumbing tubes, but when installing

this type be sure to connect the

wire to a 12-volt source activated

by the ignition switch.

Electric chokes were originally

operated by a resistance-wire

heater, but Holley began using a

solid-state heater early in 1977.

Once the engine has started, the

choke plate is moved to a partially

open or qualifying position by a

device operated by manifold

vacuum. In the case of the remote

choke versions, a diaphragm acts

on the intermediate lever. On

some models there is an expandable

link between the diaphragm

and intermediate lever to “stage”

the qualifying. In the case of

integral chokes, the qualifying is

accomplished by a piston in the

choke housing.

With both types of automatic

chokes the fast-idle cam is rotated

by the intermediate lever.

Integral choke (left) with bi-metal and housing removed to show built-in vacuum-qualifier

piston (arrow), divorced choke (right) with vacuum-qualifier diaphragm (arrow) attached

to carburetor exterior.

40

Most of these carburetors have

a tab on the throttle lever that contacts

the intermediate lever near

wide-open throttle to open the

choke. This is to clear the engine

in case it gets loaded with fuel due

to excessive cranking and is called

unloading.

Several kits are available to

modify your choke. The integral

choke can be converted to a

manual one with Part No. 45-225.

You’ll also need control cable.

Part No. 45-228 and bracket. Part

No. 45-229.

The hot-air integral choke can

be converted to electric operation

with choke cap, Part No. 45-226,

Part Nos. 45-223 and 45-224 convert

the m anual choke to

automatic electric.

One final note: Removing the

choke plate and shaft is fine for allout

competition because it

removes a restriction—gaining air

flow. Don’t do it for street applications.

Leanness during warm-up

causes damaging and dangerous

backfires.

Electric choke caps. One at top is heated

by a resistance wire (arrow). The one

below was introduced in 1977 and uses a

solid state device that raises resistance

and lowers current flow as the temperature

rises.

41

Electric-choke conversion kit 45-224 uses choke vacuum through a rubber hose. Fits R-

6299, R-6708 and 6709 four-barrels, and “47” series double pumpers (-2 or higher) such

as R-4776-2, R -4777-2, etc.

Electric-choke conversion kit 45-223 converts carburetors with an internal-choke

vacuum supply. R-1850 and R-3310 use this kit.

42

Kit 45-225 converts an integral automatic

choke to manual. You’ll also need control

cable 45-228.

A very valuable book if you work on Holley

Carburetors, it contains typical exploded

views for most models. The book is

updated yearly and is available from Holley.

Your dealer probably has one you can refer

to.

43

8 SPECIFICMODELS

List 3310 has vacuum-operated secondaries, making it universally adaptable as a performance

carburetor for 350-455 CID engines. Dual-inlet bowls and a hand choke are

features.

44

LIST 3310

One of the most popular carburetors

in the entire Holley line is

the List 3310 version of the Model

4150. One version of the carburetor

was introduced on the 425 HP

1965 Corvettes and 375 HP 1966

Chevelles —both with the 396 CID

big-block Chevrolet engine. Other

original-equipment uses of similar

carburetors have included the

famous Z-28 Camaro in both the

the 302 and 350 CID versions.

Chevrolet versions of this carburetor

have different list numbers.

Perhaps the reason for the

popularity of the 3310 is its highperformance

heritage and because

it installs easily on a wide variety

of cars with good assurance of

working well on almost any 350 to

455 CID engine. Its application

flexibility com es from the

diaphragm-operated secondaries

which allow the carburetor to

operate effectively over a wide

range of airflow requirements.

The carburetor has changed

slightly since its introduction. In

3310-1 form it is a 4150 type with

two metering blocks. Its linkage

and emission-connection features

make it universally adaptable to

Chevrolet, Chrysler and Ford V8

engine applications.

In 1976, the 3310-2 was

introduced. This lowest-cost 780

CFM Holley performance four

barrel has a 4160 metering plate.

INSTALLATION NOTES

The 3310 carburetor has a

universal throttle lever for

Chevrolet, Chrysler, and Fordincluding

automatic-transmission

models. The linkage parts shipped

with the carburetor can be combined

to create a throttle lever

exactly right for your application.

Note the center-pivot float

bowls. Each has its own inlet, so

the fuel line must connect the

stock fuel line to both inlets.

All 3310-2 carburetors have a

manual choke. If you need a choke

cable, buy a 6-foot-long hand control-cable,

45-226. Electric choke

kit 45-223 can be used if you

prefer an automatic choke.

It is assumed, of course, that a

single four-barrel intake manifold

with the 5-3/16-inch x 5-5/8-inch

bolt-hole pattern is already

installed on the car—or an adapter

will be required.

Adapters, unfortunately, are

usually “ thieves.” They steal airflow

capacity. As an example, a

3310 drops from 780 to 640 CFM

when an adapter is used between it

and a manifold with the spreadbore

pattern. It is always best to

install a carburetor which Jits the

manifold directly.

If your engine was originally

equipped with a spread-bore carburetor

(1-3/8-inch primaries and

2-1 /4-inch secondaries), use a

Holley 4165, 4175 or 4360 which

will fit without an adapter.

t

45

3310 universal linkage set up tor GM applications. Loose parts fit Chrysler.

Il'ono of these is not offered for

your particular car, however, a

4150 or 4160 with a replacement

manifold would probably be a

more practical choice. This way,

you would have all of the right fittings

and the correct throttle

linkage for Chevrolet, Chrysler

and Ford. Adapting a carburetor to

a modern-day automobile is no

easy task because there are so

many connections and linkages to

consider.

When you unpack the carburetor,

you will notice all of the hose

fittings are closed with rubber

shipping plugs. These can be left

installed when no hose will be

attached to a fitting.

The only exception is the 3/8-

inch PCV fitting extending from

the rear of the carburetor base,

just under the secondary bowl.

This plug may blow off if the

engine backfires. If the PCV fitting

is not used, replace the shipping

plug with a piece of hose plugged

at one end. The plugged hose

should be clamped onto the

vacuum fitting so it will not blow

off in the event of a backfire. If

you prefer, the tube can be closed

by filling it with an epoxy compound

such as Dcvcon. Do not

use rubber-type compounds (such

as Silastic RTV) to close such fittings

because these turn to jelly

when exposed to gasoline.

46

This is the linkage out of the box, ready to fit Chrysler applications.

This shows the Ford version. Screw has been removed to allow free-floating kick-down

lever to operate. Adjustment screw and extension spring are supplied.

\

{

47

One of the 600 CFM emission/performance carburetors. This one is List 6979 for 1973/

74 GM applications. Photo at right shows top view.

EMISSION/PERFORMANCE

CARBURETORS

In 1972, Holley introduced the

R-6619, Model 4160 carburetor.

The original idea was to provide a

“ little brother” to the R-3310,

aimed at milder street packages

and applications that see a lot of

“ lugging” or low-speed, heavyload

operation—such as recreational

vehicles (RV's). So this

number was dubbed the R V carburetor.,

which is perhaps unfortunate

because it has many more

uses. For instance, when installed

with a Holley manifold in a latemodel

vehicle with a V8 engine it

provides a good combination of

economy and street performance

in addition to meeting Federal

exhaust emission standards.

Ford, Chevrolet and Chrysler

versions of the same basic carburetor

are available, with unique

throttle levers and slight calibration

differences.

These carburetors are changed

so they remain compatible with

each model year. The first group

covered vehicles from 1970 to

1972. With the advent of exhaustgas

recirculation (FOR), Holley

developed a group of these carburetors

compatible with EGR.

There are calibration changes and

provision for an EGR signal. This

48

i

group handles 1973-74 vehicles

and separate units cover GM,

Chrysler and Ford applications. In

1977, Holley released another

group for 1975-76 vehicles with

catalytic converters, including

vans.

These carburetors have all been

developed as a system utilizing

Holley intake manifolds. They are

Model 4160s using diaphragmoperated

secondaries. The capacity

is 600 CFM with 1-1 /8-inch primary

venturis and 1-5/16-inch

secondary venturies. All four

throttle bores are 1-9/16-inch

diameter. Fuel bowls have sidemounted

floats with a single inlet

on the primary side. The choke is

12-volt electric with a solid-state

heater.

So here we have a line of carburetors

that offer economy, performance,

driveability and meet

the emission requirements of the

applicable year. Not just RV carburetors—although

they're great

for that—but truly emission/performance

carburetors. These carburetors

receive continued, concentrated

development and represent

the best 4160 street carburetors

Holley has to offer for latemodel

vehicles.

49

-- M

Last of the Model 31 60's. This one is List 391 6 which flows 950-CFM. That thing sticking

up in the middle of the air horn is a choke—believe it or not.

MODELS 3150 AND 3160

These "three-barrel'' carburetors

were conceived in the early

1960s to provide higher flow

capacity for NASCAR racing

engines. Later they were applied to

drag racing and saw some street

application.

Increased capacity was obtained

by making the primary side as

large as possible with 1-9/16-inch

venturi and 1-3/4-inch bores.

Material between the secondary

venturii and bores was removed,

resulting in oval shaped sections of

1-9/16 x 3-7/16 inches in the venturi

and 1-3/4 x 3-5/8-inches in

the bore.

T he oval se c o n d a ry is

diaphragm operated, but because

velocity and signals are low due to

the large size, a special diaphragm

assembly was designed. The

manual choke is spring-loaded

open. The air horn is cut away.

Because these carburetors were

so large, secondary-opening

characteristics were critical.

Remember, just because the secondary

plate is open doesn't

necessarily mean that the nozzles

are feeding. Venturi velocity must

be great enough to provide an adequate

metering signal. Calibration

is a little tricky, but some people

used them with great success,

especially with large engine, high

RPM applications.

Carburetor-size limitations for

the small-block engines and the

50

Large secondary operating diaphragm was necessary on 3160s to provide adequate

opening force.

introduction of the Model 4500

Dominator Carburetor for bigblock

engines signaled the end of

3160 use in NASCAR. Likewise,

the model 4500 became the more

popular way to go in drag-racing

classes that permit unlimited carburetor

size. Two 3160 models of

950 CFM (0-3916) and 1050 CFM

(0-4604) were offered for quite a

few years, but finally dropped in

1974. The added capacity of the 0-

4604 was obtained with very small

booster venturi.

If you have one of these carburetors,

hang on to it—you have

a collector’s item. The Repair and

Adjustment section also applies to

these carburetors, and Renew Kits

are still available.

Yes, there is a venturi here on the secondary

side. Not much of one, however.

51

9 CARBURETORSELECTION

More about using the chart—If

your car has an automatictransmission,

make sure you

know the converter stall speed

before using the chart. If in doubt,

use the figure shown for a typical

Chevrolet converter (1350 RPM).

If you are using a modified converter

for a racing application,

make sure the stall speed is what

you think it is.

If your car has a manual

transmission, use the lowest RPM

at which you use wide-open throttle.

This must be a very conservative

RPM (on the low-RPM side,

that is!) and should be found by

observing your own driving habits

in the vehicle involved. Watch

your tachometer! The heavier the

vehicle and the lower the numerical

axle ratio (higher gear ratio) —

the lower this RPM must be

With engines from 300 to 400

CID, the right choice usually

works out to be a 650 to 700 CFM

carburetor. A light car, Camaro,

Mustang or Duster may be able to

use a 700 or 750 CFM unit,

especially with a high numerical

gear ratio (low gear ratio).

When in doubt, select a smaller

carburetor size because it will typically

give better acceleration

times—even though power may

fall off slightly at top RPM. You

can believe that you’ll be happier

with the smaller carburetor nearly

every time!

Regardless of all the evidence to

the contrary, a lot of carburetor

buyers “ psych” themselves into

believing that bigger is better.

Thus, Holley sells more large carburetors

(800 and 850 CFM)

because of the widespread fallacy

that if a 650 is good —an 850 must

be better. This is not true!

52

CARBURETOR SIZE SELECTOR

Model 4150 Double-Pumpers

A B C

600 —

4000

650 —

- 3500 700

- 3000

- 2500

- C I D

- 200 750 _

O I

C

o

X

5

2

Q.

- 2000

- 1500

••

c

800 -

0) - 300

oTO

\

Q

G rey lin e is EX A M P LE described below

tn

. 5 "

a, - 400 850 —

C

5

c

tu

- 5 0 0

<0

O

CC

E3

E

c

2

- 1000

1050 —

- 500

INSTRUCTIONS

1. Select m inim um RPM at wide-open thro ttle In column

A; th is w ill be converter stnll speed on cars with

autom atic transm issions. Do not overestim ate RPM

In colum n A.

2. Select engine size (cubic in ches! in colum n B

3. Draw lin e between selected points in colum ns A & B.

oxtending the lin e to intersect colum n C

4. Maxim ize recom m endod carbureto r size is road

Irom point a t w hich line crosses colum n C.

EXAM PLE: 350 CID engine w ith 1350 RPM converter

sta ll speed (Typical lo r stock Chevrolet

converters I

NOTE: Applies o n ly to m echanically operated

secondaries

53

VOLUMETRIC EFFICIENCY

Volumetric efficiency (V.E., n)

indicates how well the engine

breathes. The better the

“ breathing ability’’ —the higher

the volumetric efficiency.

Volumetric efficiency is really an

incorrect description of what is

being measured. But, the term has

been in use for so many years that

there’s no real reason to try to

change the usage to the correct

term, mass efficiency.

Volumetric efficiency is the ratio

of the actual mass (weight) of air

taken into the engine—compared

to the mass which the engine displacement

would theoretically take

in if there were no losses. This ratio

is expressed as a percentage. It is

quite low at idle and low speeds

because the “ pump” or engine is

being throttled,

y ^ _ A c tu a l m ass of a ir ta k e n in

T h e o re tic a l m a s s o f a ir w h ic h

c o u ld be ta k e n in

Volumetric efficiency reaches a

maximum at a speed close to that

where maximum torque at wideopen

throttle occurs, then falls off

as engine speed is increased to

peak RPM.

The volumetric-efficiency curve

closely follows the torque curve.

EFFECT OF V.E.

After figuring airflow requirement

for an engine with 100%

volumetric efficiency, then you get

realistic about your engine and

reduce the airflow number according

to the volumetric efficienty

you expect your engine to have.

Select a carburetor rated to flow

the amount of air your engine

actually needs, taking volumetric

efficiency into account.

An ordinary engine has a V.E.

of about 75% at maximum speed;

about 80% at maximum torque. A

high-performance engine has a

V.E. of about 80% at maximum

speed; about 85% at maximum

torque. An all-out racing engine

has a V.E. of about 90% at maximum

speed; about 95% at maximum

torque. A highly tuned

intake and exhaust system with

efficient cylinder-head porting and

a camshaft ground to take full advantage

of the engine’s other

equipment can provide such complete

cylinder filling that a V.E. of

100%—or slightly higher—is obtained

at the speed for which the

system is tuned.

54

RPM

If you use this graph to find airflow requirement, multiply the indicated airflow by the

volumetric efficiency you expect from your engine. Use a carburetor with an airflow rating

equal to or slightly smaller than the airflow requirement for your engine. The text provides

further details.

55

volumetric efficiency you expect from your engine. This graph is based on a full-power

fuel/air ratio of 0.08 which is suitable for nearly all engines.

56

10 METERINGBLOCKS

O-rlng-sealed accelerator-pump transfer tube is used on all Holley four-barrels since

1975. This tube provides a positively sealed passage for the accelerator-pump shot so

none will be wasted. Note how gasket is cut to clear the tube.

Old-style metering block is shown at left in the lower photo. Any attempt to use the oldstyle

non-tube metering block with the newer gasket will draw fuel from the acceleratorpump

system and a full-rich mixture will be supplied to the engine.

57

Description of holes and passages in metering block. Top photo shows side which mates

to main body gasket. Lower photo is bowl side of metering block.

I -Accelerator-pump-discharge passage

2- Timed-spark passage (see 12)

3 - Curb-idle discharge

4 - ldle-transfer fuel connects to main body and to curb-idle-adjust screw

6 - ldle bleed air enters from main body

7 - Main passage to discharge nozzle

8 - Main-bleed air enters from main body

9 - Dowels to position block & gasket

I I -Bowl-vent passage

12-Timed-spark tube boss

13 - ldle-mixture-adjustment needle

1 4 - Main jet

15 - Power-valve threaded opening

1 6 - Power valve

17-Power-valve-channel-restriction (connects to main well 21)

18- Manifold vacuum chamber (for power valve operation)

1 9 - ldle down well

20- ldle well

21- Main well

22- Air-bleed holes into main well

23- Main air well

24- ldle fuel from main well

25- ldle feed restriction to idle well

2 6 - Fuel entry from accelerator pump in fuel bowl

Description of holes in main body to metering block gasket surface:

1- To discharge nozzle (accel. pump) 7- To main discharge nozzle

2- To timed-spark port

8- To main air bleed

3- To curb-idle discharge

9- Dowel locators for metering block

4- To idle-transfer slot

10- Not used

5- Used only with auxiliary idle air bleed 11 -To bowl vent (pivot tube)

6- To idle air bleed

59

11 REPAIRAND ADJUSTMENT

PREPARATION FOR

CARBURETOR REPAIR

Once you've analyzed your

engine problem and have decided

it lies with the carburetor, you've

set yourself up for another decision.

Here are your options:

1. Take the carburetor apart,

make the critical repair and put it

back together.

2. Make an economy repair.

3. Perform a complete carburetor

disassembly and repair.

If you’re fairly sure where the

problem lies and time is important,

option 1 is probably the best

approach. You might be able to

perform this operation without

removing the carburetor, but it

isn’t really the best idea. Bending

over the fender can be difficult and

it’s easy to lose parts.

If time allows, remove the carburetor.

For this option you need

a gasket kit at the very minimum.

Gasket-kit numbers are listed in

the Holley Illustrated Parts and

Spec Manual. Your dealer probably

has one. These inexpensive

manuals contain a wealth of information

about specific Holley carburetors

and can be obtained by

writing:

Sales Department

Holley Replacement Parts

11955 E. Nine Mile Road

Warren, Michigan 48090

SO YOU THINK YOU'VE

GOT A VACUUM LEAK?

Air leaks are commonly called

vacuum leaks: however, this

term is really in a c c u ra te -

vacuum can't really leak. Air

leaks into the vacuum —intake

manifold in our case—and that

causes problems.

The first step in finding an air

leak is recognizing it. Depending

on the size of the leak, the

symptoms are fairly simple. The

engine w ill idle rough or

“hunt” —refuse to idle at one

speed. You can check for a leak

by partially closing the choke; if

the engine runs better, you’ve

got an air leak. Occasionally, if

the leak is bad enough, the

engine won’t idle at all.

Roughness at idle is caused

by the engine getting more air

than it needs, leaning out the

mixture. Vacuum (air) leaks

show up more at idle than any

higher engine speed simply

because the engine is receiving

so little fuel/air mixture that the

added air drastically changes

the fuel/air ratio. At higher

engine speeds the amount of air

leaking in is such a small

amount compared to the total

fuel/air mixture that the leak

seems to disapper.

Unlike oil leaks, air leaks can't

be seen, so you’ve got to find

some other way to locate them.

60

Sometimes they can be heard,

but it’s really hard to pinpoint

one without putting your ear

near a hot, running engine—

definitely not recommended. So

how do you find an air leak?

Spray carb cleaner.

In a d d itio n to its o th e r

praiseworthy qualities —like

cleaning carburetors and clearing

sinuses—spray carburetor

cleaner is excellent for finding

vacuum leaks.

Keep in mind that carb cleaner

is extremely flammable and

should only be used in a well

ventilated area. It also has a terrific

appetite for paint—even

heat resistant —so keep the

overspray down.

Use the kind of cleaner with

the long plastic tube that snaps

into the nozzle. This gives a

much more accurate spray. With

the engine idling, spray the parts

you think might be leaking, one

at a time. Just a short spurt is all

that is needed. Be sure to let the

air clear before you spray again.

If you spray near an air leak, the

engine will momentarily smooth

out and gain about 200 RPM.

If you have no idea where the

leak is, start with the most likely

places. Check the vacuum-hose

connections first. If you've

removed the carburetor, spray

around the base gasket.

When checking for air leaks,

don't trust your eyes. A quick

glance won’t reveal a crack in a

vacuum hose or a split gasket. If

this test says you’ve got a leak at

a vacuum connection, take a

careful look. If you still can't see

anything after a close inspection,

spray around the part, or

from another angle. Sometimes

the spray will “ bounce” and indicate

a leak at one place when it’s

really close by.

This same technique can be

used to check for worn throttleshaft

bores. The shafts and their

bores wear with use, but the

change is not nearly so apparent

as disconnecting a vacuum

hose, but the result is the

same—an air leak and a lumpy

idle.

Check for a worn throttle shaft

and bore the same way you

check for any other air leak.

Spray the carb cleaner directly

at the throttle shaft where it

enters the throttle body.

Because the linkage-side of the

primary shaft wears the most,

check there first. Holley carburetors

with diaphragm secondaries

use Teflon bushings in

the secondary throttle-shaft

bores, so if the secondaries are

excessively worn, chances are

the primaries are shot.

There’s really no way to check

them when the carburetor is off

the car. A slight amount of wear

on the throttle bores is normal,

and the only real test is to see if

the engine will idle. Larger

engines can tolerate more wear

before causing problems.

If the throttle bores are worn

excessively, new throttle bodies

are available from Holley for

most of their carburetors. If a replacement

is not available for

your carb, you may be able to

have yours rebushed. Check

with a machine shop, but keep in

mind, it can be expensive.

61

It is seldom necessary to resort

to option 3, disassemble the carburetor

and soak it in a special

cleaner as most manuals and

printed instructions direct you to

do. First of all, it is very time consuming.

Most subassemblies must

be taken apart, because non-metal

components cannot be exposed to

the cleaner. Commercial carburetor

cleaners are expensive, so

unless you plan to do several carburetors

or are in the business of

carburetor rebuilding, this procedure

is terribly expensive.

I feel option 2—the economy

carburetor-repair method—represents

the best combination of cost,

time, and results. Cleaners such as

kerosene, Stoddard solvent and

mild paint thinners allow you to

clean plastic, synthetic, and metal

parts together, making complete

disassembly unnecessary.

Before you disassemble your

carburetor, keep in mind that

several metering-block, meteringplate

and fuel-bowl gaskets are

used with the 4150/60 carburetors.

Unfortunately, few are interchangeable.

When disassembling

your carburetor, keep the old

gaskets to compare to the new

ones. You want to be sure to replace

the gaskets with the correct

new ones.

Holley Performance Parts

Catalog lists gasket numbers for

most popular carburetors. Holley

Illustrated Parts & Specs Manual

lists gasket and Renew Kit numbers

for all Holley carburetors.

Some Renew Kits contain more

than one type of gasket so one kit

can be used to service several carburetor

numbers.

Some original-equipment

gaskets are adhesive-treated for

improved sealing. Extra effort may

be required to disassemble carburetors

with these gaskets.

To make things less confusing,

the available gaskets are shown

here with information on their

general use. Mating holes for locator

pins on the metering blocks

ensure that gasket openings will

line up with those in the metering

plate or fuel bowl. If the gasket

looks like it doesn't fit, flop it over

and try it again.

Cork gaskets with vertical slots

on each side can be replaced by

either gasket 1 or 2, depending on

the center section. New, harder

gasket material eliminates the

need for the slots.

Also, Holley markets these

gaskets in sets for popular applications.

When buying gaskets in

bubble packs, the part number will

include BP instead of R. For instance,

live 8R-1023 gaskets are

sold as bubble pack 8BP-1023. See

the performance catalog.

A small open can, a brush, a

small scraping tool and some

elbow grease let you do a fine job

of washing. For dissolving

deposits use lacquer thinner,

toluol, MEK, Gum-Out, Chem-

Tool, etc. These must be used in a

well-ventilated area away from

fire. Be aware of pilot lights such as

those on a gas range, water heater

or furnace. Wear safety glasses and

keep your hands out of any dissolving-type

chemicals.

62

8R-1779 or 8R-1907 Primary-meteringblock

gasket for most Model 4150 and

some 4160 carburetors. It is also used as a

secondary-metering-block gasket on double-pumpers.

This gasket is not used

where there is an accelerator-pump

transfer tube.

8R-1781 or 8R-1909—Use on same carburetors

as gasket 1 when they are equipped

with an accelerator-pump transfer

tube. This gasket is used on a few 4150

carburetors and on the primary side of

some 4160’s. Gaskets 1 and 2 are not interchangeable,

but a 2 can be made from a

1 by cutting a half circle in the center section

to clear the transfer tube.

8R-1780 or 8R-1908—Secondary fuelbowl

gasket for Model 4160 carburetors.

8R-1594 or 8R-1906—Primary meteringblock

gasket for Model 4160 Chrysler

applications beginning in 1968.

8R-1784 or 8R-1912 —Primary metering 8R-726 —Secondary metering-plate

block gasket for Model 4160 Chrysler car- gasket for some Model 4160’s.

buretors with accelerator-pump transfer

tube. Gaskets 4 and 5 are not interchangeable,

but you can make a 5 from a 4 by cutting

out a half circle to clear the transfer

tube.

63

7

8R-1 437 —Secondary metering-plate

gasket for Model 41 60 Chrysler.

8

8R-1783 or 8R-1911-Fuel-bowl gasket

for Models 4150 and 4160 carburetors.

Use cleaner with a brush on

large surfaces to dissolve deposits.

Use a common ear syringe to

shoot the solution through

passages. One way or another, you

can do a good job without exotic

equipment.

Passages and orifices should be

blown out with compressed air. If

compressed air is not available,

you can always use a bicycle or tire

pump. Never use a wire or drill to

clean orifices and restrictions

because the slightest mark can

change How characteristics.

For options 2 and 3, you should

obtain the right Renew Kit listed

in the Parts and Spec Manual,

catalog or Performance Carburetor

Renew Kit listed in the Holley

Performance Carburetor Catalog.

Both catalogs are available at the

previously-mentioned address for

a small sum. Holley repair kits

contain the same components as

used in the original-equipment

carburetor.

The kit contains all gaskets

including the one between the carburetor

and intake manifold. Also

included are fuel inlet valves,

power valves, accelerator-pump

diaphragms and an instruction

sheet giving adjustment specifications

and procedures.

Parts will probably be left over

from your kit when you’ve

finished. Don’t panic! In most

cases, the kits are designed to service

more than one application.

This ‘’consolidation” reduces the

number of kits the dealer has to

stock. It is actually more economical

to include a few extra parts so

64

Contents of a typical 4-barrel Renew Kit. Be sure to read the instruction sheet. It contains

a lot of tips and most of the adjustment specifications you’ll need.

Most carburetors are identified at this location. The "LIST 6979" is an engineering number.

Holley Engineering releases a parts list to their production plants and the carburetor

is built to that detailed list. Hence the name “List.”

Some normal replacement carburetors are catalogued and packaged under different

"Sales" numbers, but the engineering list or part number is always the one stamped on the

carburetor. Specification information in the various Holley literature also refers to the List

number.

The lower stamped number is the manufacturing date. The first three numbers are the

day of the year. 055 means the 55th day or February 24. The last number is the year (6 for

1976).

65

each kit will service several

different carburetors.

Special tools are fine if you plan

on working on a lot of carburetors

or going into the repair business.

Common tools are usually good

enough for carburetor disassembly

and repair. You will need standard

and Phillips screw-drivers, regular

and needle-nose pliers and the

usual set of open-end wrenches. A

sharp scraping tool is good to have

around for removing deposits and

old gaskets. Be very careful with

carburetor sealing surfaces; zinc

and aluminum are easily

scratched, and scraping can also

remove sealing beads. A special 1-

inch open-end wrench (MAC S-

141) is required to remove the

fuel-inlet fitting, but you can

sometimes make do with a standard

open-end wrench. Corbinclamp

pliers and flare-nut

wrenches are good to have for carburetor

removal and installation.

Flare-nut wrenches are a necessity

if you are working with soft fuelline

nuts.

I can’t overstress the importance

of tagging and identifying

each vacuum hose with a piece of

tape or a shipping tag. Take a few

minutes to make a schematic

diagram showing all of the hookups.

This will save a lot of grief,

especially on later vehicles with

complicated emission-control

systems. Follow the kit instructions

for removing and installing

the carburetor.

Once you've removed the carburetor,

a holding fixture should

be used to prevent damage to the

throttle plates. Many of these

stands or fixtures are available,

but four 5/16-inch bolts and nuts

work just fine on any carburetor

with four mounting holes. A

second nut can be used on each

bolt to lock the throttle body onto

the bolts to prevent wobble.

1/Before beginning disassembly, mount

carburetor on a holding fixture or a set of

5/16-inch bolts, or onto Holley Carburetor

Legs. It’s a good idea to loosen the fuelinlet

fitting, the fuel-bowl sight plugs and

inlet-valve lock screws now because it is

easier to do while the carburetor is completely

assembled. I prefer to loosen these

parts while the carburetor is still securely

bolted to the manifold.

66

2/Remove the four secondary fuel-bowl

screws. Remove fuel bowl, metering block

and their gaskets. On model 4160 carburetors,

remove the clutch-head screws and

metering plate. Separating these assemblies

may require a rap from your

screwdriver handle or a rubber or plastic

mallet.

The carburetor I'm using here has dual

inlets (Model 4150 style) and no fueldelivery

tube between bowls.

3/Here is a single-inlet carburetor with the

balance tube between the bowls. Note the

0-ring (arrow). Don't worry about preserving

the 0-ring if you are rebuilding—new

ones are in the repair kit. Just slide the fuel

bowls off the tube.

When reassembling, use petroleum jelly or

oil on the O-rings. Twist tube slightly to

ease entry of O-ring into each bowl assembly

Ṁake sure no part of the O-ring gets

pinched over the bead of the tube. Fuel

under pressure is contained in this tube, so

don't make any mistakes or you could end

up with a leak.

4/Now repeat the procedure on the primary

side.

Use plenty of torque when replacing the

bowl screws—50 in. lb. if you're fortunate

enough to have an inch-pound torque

wrench with a screwdriver-blade attachment.

67

5/Next remove the choke unit. With

integral chokes, the first thing to do is to

remove the little hairpin retainer from the

bottom of the rod connecting the chokecontrol

to the choke lever. Needle-nose

pliers are best for this.

6/Before going further, note where the little

mark on the black bimetal housing is

relative to the marks on the top of the

choke casting. The little strut in the middle

of these marks on the casting is called the

in d e x mark. Choke adjustments are designated

relative to this mark. Draw a picture

so you can reassemble the choke in the

same position. Choke settings are called

out in marks rich or lean from the index.

Consult the Holley Spec Manual if you've

lost or forgotten the setting.

7/Remove the three screws holding the bimetal

housing retainer and remove retainer,

gasket and housing. Do not remove the bimetal

from the housing.

f.

68

8/The metal choke housing can be

removed from the main body by the removal

of three attachment screws.

9/For those carburetors with a divorced or

remote choke, remove the two screws

holding the choke diaphragm, the retainer

holding the fast-idle cam and lever and the

choke-rod retainer if there is one. Disconnect

vacuum hose at the throttle body and

remove all of the choke parts. This photo

shows the choke lever and diaphragm from

a typical divorced- or remote-choke

application.

10/Remove clip from shaft (arrow) and

take out 3 screws mounting diaphragm

housing to main body. Remove diaphragm

housing.

69

11/Take out the 8 screws attaching throttle

body to main body. These are often

tough to turn. An impact driver is quite

helpful here.

FUEL BOWLS

12/Center-pivot float fuel bowls hinge the

primary floats at the front and secondary

floats at the back. This type bowl can have

either single or dual inlets. When both sides

of the bowl casting are tapped, one side is

closed with a plug and the other side has an

inlet fitting. Center-pivot float bowls

always have externally adjustable needle/

seat.

13/On bowls with front-mounted floats,

first remove the inlet-valve assembly.

Loosen the lock screw and turn the hex-nut

counterclockwise. The hex-nut slips over

the inlet-valve assembly. Now remove the

two screws holding the float-mounting

bracket and remove the bracket and float

from the fuel bowl.

14/Fuel bowl with side-mounted float.

Remove baffle (arrow) surrounding inlet

valve and then retainer from float hinge pin.

Float assembly can then be removed. Nonadjustable

inlet valves must be removed

from the inside with an open-end wrench.

Take out the fuel-inlet fitting you previously

loosened. Remove it with the integral

filter and spring (see picture above right).

Remove sight plugs if they are used. You

now have the fuel bowl completely disassembled.

This fuel bowl has an externally

adjustable inlet-valve.

70

15/Disassembled side-mounted-float fuel

bowl. This one has a non-adjustable inlet

valve.

16/1 7/Primary bowls (and secondary

bowls on double-pumpers) contain

accelerator-pump assemblies. Remove

four attachment screws and lift pump

diaphragm and housing from the bowl.

Some accelerator pumps have a rubberumbrella

inlet valve (top photo). If you plan

to immerse the fuel bowl in cleaner, the

rubber valve must be removed.

Other pumps have a hanging-ball inlet.

Clearance between ball and retainer

(arrow) should be 0.011—0.013 inch

measured with a wire gauge or drill bit with

bowl inverted. Clearance is adjusted by

bending retainer tab.

18/Remove main-metering jets with a

wide-blade screwdriver. The screwdriver

must completely bridge the slot or you will

damage the jets. Primary and secondary

jets are often different sizes. Small jets go

in the primary side if the carburetor has

smaller primary venturis.

On rare occasions jets will differ from

side to side in the same metering block.

Always check the jet sizes and locations

and write this down b e fo re you take the

jets out.

DO NOT REMOVE ANY PRESSED-IN

VACUUM TUBES. Remove bowl-vent

splash shield and any vacuum fittings if

used. Take out idle-mixture screws and

seals. Remove power valves with a 1 -inch

wrench. A socket wrench is preferred, but

you can do it with an open-end if you proceed

carefully. The wrench for large fuelinlet

fittings works fine here.

71

It is not usually necessary to disassemble

metering blocks any further. Although

there are tubes inside the main and idle

wells, these can usually be cleaned with

compressed air. The small metering plate

from the secondary-side of a Model 4160

requires no further disassembly.

Metering blocks with an 0-ringed tube

connecting them to the main body should

have this tube removed before proceeding

further.

Use new gaskets on reassembly. If you

have to use the existing gaskets, keep

them soaking In gasoline or solvent so they

will not shrink and/or lose their shape.

When you reassemble the carburetor,

install the mixture screws 1-1/2 turns off

their seats as a starting point

19/Remove four attachment screws. A rap

will separate the upper and lower housings.

The spring and diaphragm can now be

removed. My pencil is pointing to a cork

gasket that should be replaced on

reassembly.

20/21/Take a good look at the choke

assembly before taking it apart. Note the

fast-idle cam and choke-lever relationship.

These must go back together in the same

position.

Remove the choke-shaft nut, lock

washer and spacer and then slide the shaft

and fast-idle cam from the housing. Next

remove the choke qualifying piston. Make

sure it operates freely in its bore. If it

doesn't, it can be cleaned and polished with

crocus cloth.

Remove the cork gasket that surrounds

the restriction on the back side of the

choke housing. Use a new gasket on

reassembly.

72

22/Choke-shaft removal is seldom necessary and I don't recommend it, but if you plan to

immerse the main body in a carburetor cleaner, you must remove the choke and shaft to

remove the little plastic guide. File the staked portion of the choke screws, then take out

the screws and lift the choke plate out of the shaft. Remember, the choke-plate screws

must be restaked upon reassembly. This requires supporting the shaft so it will not bend.

Remove the pump-discharge-nozzle screw, the nozzle and gasket. Turn the body over

to remove the pump-discharge valve. Double pumpers have two pump-discharge assemblies.

23/lt is seldom necessary to disassemble

the throttle body and immerse ail of the

parts. First of all, only a few metering

restrictions and small passages are in the

throttle body. Secondly, the throttle-plateattachment

screws must be removed and

restaked upon assembly. This all adds up to

quite a task. If it isn't necessary, why do it?

Cleaning with a brush and a milder solvent

is usually more than adequate.

If you insist on a complete disassembly,

here it is: Remove the idle-speed screw

and spring. Remove the diaphragm-operating

lever from the secondary throttle shaft

and the fast-idle lever from the primary

shaft. Remove the cotter key and the connecting

link between the primary and secondary

throttle levers. File off staked ends

of the throttle-plate attachment screws,

remove screws and throttle plates. Slide

the shafts out of the flange. Take out the

Teflon bushings (typical on secondary side

of carburetors with diaphragm-operated

secondaries).

73

CLEANING AND ASSEMBLY

Now your carburetor Is completely disassembled and ready for cleaning. Remember, if

you’ve chosen the complete carburetor repair method, only the metal parts should be

immersed in the special cleaner.

All non-metal parts, including the choke bimetal and housing, Teflon bushings and the

plastic accelerator-pump cams should be cleaned with a milder cleaner such as kerosene.

Once all cleaning is done inspect the parts for undue wear to determine if they should be

replaced. If you've purchased the Renew Kit, all gaskets, pump diaphragms, secondary

diaphragm (in some cases), fuel-inlet valves and power valves are included.

In reassembling the carburetor, simply follow the disassembly instructions in reverse

order. Pictures and exploded views in this book should be very helpful. There are a few

things to look for.

When assembling the fuel-supply tube, use a little Vaseline on the O-rings so they’ll slip

In a little easier. When assembled properly, you should be able to rotate the tube with your

fingers.

Be sure to do a good job of restaking the choke and throttle attachment screws. If one

of these screws comes loose and goes into the engine, it could be very expensive. Other

than the very small choke and throttle screws, don't be afraid to torque the assembly

screws down, especially the throttle-body and fuel-bowl screws. Once you have them all

in, it’s a good idea to go around again and give them a little extra.

24/Be sure the secondary diaphragm is

sealed all the way around when you attach

the cover to the lower housing. Unload the

diaphragm spring by pushing up on the rod.

This will cause the diaphragm to lay flatter

and make it easier to get the screws and

cover installed.

25/Some bimetal springs have a hooked

end while others have a loop as shown.

Make sure you capture the tang with the

end of the bimetal. Rotate the bimetal

housing back and forth before tightening

the retainer. The choke plate should move

as you do so.

ADJUSTMENTS

A number of adjustments need to be made

as you reassemble the carburetor. Adjustment

procedures are shown in the accompanying

photographs. Specific dimensions

are in the instruction sheet supplied with

the Renew Kit and in the Holley Spec

Manual.

74

26/For bowls without external adjustment, adjust the float by bending the tab as shown.

Be careful not to mar the contact surface. Dry-float setting is usually measured between

the bowl casting and the end of the float with the bowl inverted. Holley Renew Kits give

the correct spec and in some cases include a gage. The Holley Spec Manual is another

good source for specs.

27/Pump lever should always be capable of at least 0.01 5 to 0.020-inch additional travel

beyond the screw when the throttle is in the wide-open position. Screw and lever should

also be In contact at idle. Use screw to accomplish both. This pump cam is in position 2

(arrow). To reduce capacity and change delivery somewhat, remove screw, move cam and

insert in hole 1 and screw into alternate hole in cam. With a green cam, added lever travel

should be 0.010 inch.

75

28/Externally adjustable fuel-bowl float

levels can be set on the vehicle- Remove

the sight plug. Loosen the lock screw at the

top of the assembly and turn the adjusting

nut until the fuel level is at the bottom of

the sight-plug hole. Clockwise lowers the

fuel level, counter-clockwise raises it.

Flush the bowl by revving the engine a

few times with the transmission in neutral

to confirm your setting. Tighten the lock

screw while holding the adjustment nut and

replace the sight plug. This operation is

difficult to do accurately on a rough-idling

vehicle.

29/Choke-qualify adjustment. Specification

is clearance between the choke plate

and the casting on either the top or bottom

edge as noted. Repair kit or Holley Spec

Manual gives this dimension. Hold choke

plate closed and measure the clearance

with the diaphragm operated by hand or

with a vacuum source. A vacuum source is

best—your engine is an excellent one.

Adjust by bending the diaphragm link on

divorced-choke carburetors.

Integral-choke carburetors have a screw

adjustment on the choke housing.

30/Dechoke spec is measured between

choke plate and housing with the throttle in

the wide-open position. Adjust by bending

the end of the choke rod as indicated by

screwdriver.

31/Emission-type vent valve connects to

charcoal canister. Clearance should be

0.01 5 inch as shown with the throttle at

normal or curb idle. Adjust by bending lever.

Old-style external vent clearance called

out in Holley Spec Manual and repair kit Is

usually around 3/32 inch. Adjust by bending

lever.

76

32/Normal or curb idle is set as shown.

You'll want to set it to correct engine RPM

later, but about 1-1/2 turns from having the

plates seated in the bores is a good rough

setting.

33/Secondary idle-speed adjustment.

About 1/2 to 1 turn away from having the

plates seated in the bore is a good approximation.

34/Fast-idle adjustment is made with the

fast-idle screw on the highest step of the

fast-idle cam. Clearance between the primary

throttle plate and the throttle bore

should be about 0.025 inch, measured as

shown.

35/Dashpot setting refers to the additional

travel the dashpot has when the throttle Is

in the curb-idle position. Consult the Holley

Spec Manual for the exact setting, but

0.090-0.120 inch is common. Adjust by

loosening the locknut and turning the complete

dashpot assembly.

77

EXPLODEDVIEW

Model 4 1 5 0 /4 1 6 0 Exploded V iew

(a lio 3150/31601

Holley Typical View 24-1

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Index

A

Accelerator pump, 26IT

adjustment 75

cam 31

capacity 28, 29

capacity (table) 30

diaphragm-type 27, 28

disassembly 71

discharge nozzles 28

“ R E O " 29

A ir leaks, 60, 61

American Motors 5

Available sizes o f 4150/60 4

B

Boost vcnluri 19. 20

Boost venturi, annular discharge 21

c

Camaro 44

Carburetor sizing 52ff

air requirements 54, 55

for mechanical secondaries 52. table, 53

fuel requirements 56

Chevrolet 4, 5, 45-49

Choke

qualify adjustment 76

shaft, removal o f 73

system 38fT

assembly 74

automatic 39ff

conversion kits 42, 43

electric 40, 41

internal 39, 40

qualifying 40

remote 39

removal and disassembly 68, 69, 72

removal o f 41

types o f 39

Chrysler 5, 45-49

Conversion kit 4, 5

Corvette 44

D

Disassembly 66ff

E

E m is s io n /P e rfo rm a n c e senes 48. 49

s p e c ific a tio n s o f 49

F

Float setting, 75

Ford 2, 4, 45-49

Fuel bowls

disassembly 70. 71

vent, adjustment 76

primary 7

removal 67

H

Hot Idle Compensator 15

I

Idle system

“ reverse'' 14. 15

12IT

adjustment 13, 14

air bleed 14. 15

transfer passages

adjustment 77

Inlet system 6ff

Boat, brass 7, 8

Boat, synthetic 7, 8

fuel bowl

front-mounted 7, 8

side-mounted 7, 9

inlet valve 6IT

externally adjustable 9, 10

internally adjustable 10

sizes 10, II

L

List numbers, explanation o f 65

List 3310 44IT

installation 45, 46

specifications 44, 45

M

Main jets 17, 18

Bow 17. 18

numbering system 18

Main metering system I6 ff

air bleed 18-20

Metering blocks 571L

description o f passages 58. 59

disassembly 71, 72

gaskets, description o f 62-64

Model 4500 “ D om inator" 51

Models 3150, 3160 “ three-barrels'' 50, 51

N

NASCAR 50, 51

P

Power system 220'

Power valve 22-24

rating 24

removal 24

staged 24, 25

Power-valve-channel restriction (PCVR) 22, 24

R

Repair and adjustment 60ff

s

Secondary diaphragm

assembly 74

disassembly 72

Secondary system, 32IT

diaphragm-type 5, 32-34,

tuning 33,34, advantages o f 35

mechanical 4, 5, 33-34, 36, advantages o f 37

Secondary-metering system 3

T

Throttle body, disassembly 73

V

Vacuum leaks, 60, 61

Vacuum trends 19

Venturi 19. 20

Viton, 9, 10

Volumetric efficiency 54

z

Z-28 44

80 D-8.322510525

5 1 1 0 0 >

9 780895 860477

ISBN 0-flT5Ab-04?-3

KNOW YOUR HOLLEY 4150/4160

llolkii Carburetor/

& manifold/

High-perform ance A stock replacement

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Accelerator-pump system , page 29.

Concise text explains the basics of the fuel-inlet,

idle, main-metering, power, accelerator-pump,

secondary and choke systems. Learn about the

4150/4160’s unique metering blocks. Covers carburetor

repair and adjustment. Bonus section describes

how to choose a carburetor based on engine

size and volumetric efficiency. More than 100

photos, charts and drawings show you how to do it

right.

External float adjuatment,

page 76.

$11.00 u.s.

$16.00 CAN

ISBN 0-fl'15flLi-047-3

Holley 4150 &amp; 4160 Manual

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