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Carb Tech 101
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Photo 1: This model 1407 Edelbrock carburetor replaces a ruined Rochester Quadrajet on this 1970 455 cubic-inch Buick engine.
Although it’s hard to believe that nearly 20 years have passed since the last carburetor was installed on a mass-produced vehicle, carburetors are still the fuel system of choice for many off-road, street performance and track racing enthusiasts.

In response to the performance market, aftermarket fuel system companies are now selling newly-designed carburetors, updated versions of old carburetors, remanufactured carburetors, new OE replacement “muscle car” carburetors and custom-built racing carburetors that will fit the requirements of any performance application.

To help you understand how to optimize the performance of carburetors used in performance applications, we’ll cover the basic operating principles and adjustment procedures for several popular aftermarket and original equipment lines of carburetors including Edelbrock, Holley, Rochester and Motorcraft. Because of its simplicity and ease of repair, I’ll begin by using an Edelbrock model #1407, 750 cfm, non-emission four-barrel carburetor to illustrate the basic principles of carburetor operation and adjustment. See Photo 1.

The Carburetor Venturi
A venturi is a short, rounded, hour glass-shaped tube designed to draw fuel from the carburetor float bowl into the air stream flowing through the carburetor. The air passing through the tube at its narrowest point accelerates in speed and creates a negative pressure differential between the fuel in the carburetor float bowl and the air in the venturi.

Atmospheric air pressure in the float bowl then pushes fuel through the main metering jet into the negative air pressure in the venturi. Greater fuel metering accuracy and mixing capability is achieved by mounting a “booster” venturi inside the carburetor’s main venturi.  

If the main venturi is too large for a particular engine application, the air pressure differential in the venturi will not be sufficient to draw fuel from the carburetor float bowl. The result will be a fuel metering “stumble” caused by inadequate air speed through the carburetor venturi.

To maintain a constant depression (vacuum) in the intake manifold as the secondary throttle plates open, several Edelbrock and Carter series carburetors may incorporate a set of weighted auxiliary throttle plates or spring-loaded air valves in the secondary throttle bores to maintain a slight pressure differential in the intake manifold as the engine accelerates.

Intake Manifold Vacuum
The term “intake manifold vacuum” describes the air pressure differential existing in the intake manifold when an engine draws air around a partially closed throttle plate. This air pressure differential is reduced as the throttle plate opens to allow more air volume to fill the manifold.

At wide-open throttle (WOT), the pressure differential is nearly equalized, but due to the inherent restriction of the carburetor main venturi and booster venturi, the air pressure inside the intake manifold remains slightly less than atmospheric pressure.

The Float System
The carburetor float, float needle valve and needle valve seat assembly maintain the correct fuel level in the fuel bowl. A low float level will cause a mild lean condition while a high float level will cause a mild rich condition due to the relative pressure differentials that the venturi must develop to lift the fuel out of the float bowl.

High and low fuel pump pressures influence the float level in the same way, with high fuel pump pressures tending to increase float levels and low fuel pump pressures decreasing float levels. In general, fuel pressures tend to range from 3 psi for small import engines to as much as 8 psi for full-bore drag race engines. Most carburetors perform very well with 5-6 psi of fuel pump pressure.

The Choke System
A choke plate mounted over the primary throttle bores is used to enrich air/fuel ratios for cold starting by restricting air flow into the carburetor. The choke system usually includes a thermostatic coil or hand cable to activate the choke valve, a fast-idle cam on the throttle plate to increase idle speed during engine warm-up, and a
vacuum-activated choke pull-off to open the choke valve a predetermined amount after the engine starts.

photo 2: the transition slot is exposed when the throttle plate begins to open.
Photo 2: The transition slot is exposed when the throttle plate begins to open.
The Six Metering Systems
Air flow through a carburetor venturi changes drastically as the engine accelerates from an idle to a wide-open throttle or peak engine-speed condition. To achieve a nearly “stoichiometric” or chemically perfect 14.7:1 air/fuel ratio, the carburetor must coordinate fuel flow with air flow.  

To accomplish this, a typical carburetor uses six different metering systems to achieve stoich in the fuel delivery curve: the idle, transition (off-idle), accelerator pump, main metering, air bleed and power enrichment circuits.

Because the six circuits may overlap each other as the engine accelerates, the actual air/fuel ratio may vary throughout the speed and load range of the engine. In most cases, a carburetor must run slightly richer than “stoich” to avoid lean spots in its fuel delivery curve as it transitions from circuit to circuit.

The Idle, Transition and Accelerator Pump Circuits
The idle circuit consists of two tapered idle mixture adjustment screws that thread into small round ports located under the carburetor’s primary throttle plates. The primary idle circuit draws air and fuel into an emulsion tube, which mixes gasoline drawn through the carburetor’s primary main metering jet with air drawn from an air bleed
photo 3: the accelerator pump circuit provides a temporary enrichment of air flowing through the carburetor venturi.
Photo 3: The accelerator pump circuit provides a temporary enrichment of air flowing through the carburetor venturi.
located in upper part of the primary carburetor body or booster venturi.
 
A transition “slot” circuit is located above the closed throttle plate. As the throttle plate continues to open, the transition slot adds fuel to the air rushing around the throttle plate. See Photo 2.

The transition slot draws its fuel from the idle circuit emulsion tube. As the throttle plate continues to open, fuel flow through the idle and transition circuits slows as the air pressure differential under the throttle plate decreases.

Keep in mind that, because liquid fuel flowing from the carburetor float bowl accelerates slower than the air flowing through the carburetor venturi, the carburetor will momentarily run lean until the venturi begins to draw fuel from the float bowl. To prevent the engine from developing a lean stumble during acceleration, an accelerator pump circuit is used to supply a short burst of fuel into the air flowing through the venturi. See Photo 3.

To achieve a relatively accurate fuel metering curve as the engine accelerates, the volume and duration of fuel
photo 4: all fuel flowing into the idle, transition and main metering circuits flows through the main metering jet.
Photo 4: All fuel flowing into the idle, transition and main metering circuits flows through the main metering jet.
flowing through the accelerator pump nozzles are controlled by the mechanical length of the pump stroke, the spring pressure exerted on the pump piston, and the diameter of the accelerator pump nozzles located in the main venturi.

Main Metering and Air Bleed Systems
Creating close to a 14.7:1 stoichiometric or chemically correct air/fuel mixture ratio is a difficult assignment for a mechanically controlled carburetor. But carburetors come very close to creating “stoich” by employing a very sophisticated method of mixing air with fuel before the fuel enters the venturi air stream.

Fuel is drawn through the primary venturi’s main metering jet into a main metering emulsion tube. See Photo 4.

The emulsion tube is a part of the booster venturi and is inserted into a main metering well located in the body of the carburetor. Like the idle jet emulsion tube, the main metering emulsion tube draws air from a secondary air bleed and combines it with fuel drawn through the main metering jet. This “emulsifying” action prevents liquid fuel
photo 5: air bleeds should be kept clean as part of regular carburetor maintenance.
Photo 5: Air bleeds should be kept clean as part of regular carburetor maintenance.
from being siphoned into the venturi air stream. See Photo 5.

Air bleeds perform the additional function of “curving” the air fuel mixture ratio so that the air fuel ratio remains relatively constant throughout the engine’s entire speed and load range. Without air bleeds to dilute the fuel stream with air, the carburetor would tend to run rich at peak engine speeds and loads.

Power Enrichment Systems
Internal combustion piston engines generally require rich air/fuel ratios only at wide-open throttle operating conditions. At part throttle, a carburetor delivers its best fuel economy at 15:1 and numerically higher lean air/fuel ratios. Keep in mind that, due to differences in air and fuel delivery to individual cylinders, we’re speaking of average, not absolute, air/fuel ratios when dealing with carburetors.

To vary the air/fuel mixture ratio, many carburetors like the Edelbrock 1407 restrict fuel flow during closed-throttle, high manifold-vacuum conditions by inserting a stepped metering rod into the primary main jet. Typically the
photo 6: the model 1470 carburetor has three accelerator pump volume positions drilled into the accelerator pump arm. the inside hole delivers maximum pump volume.
Photo 6: The model 1470 carburetor has three accelerator pump volume positions drilled into the accelerator pump arm. The inside hole delivers maximum pump volume.
metering rod steps are of two diameters, such as the 0.071” and 0.047” diameters on our model #1407 Edelbrock carburetor.

A calibrated spring under the metering rod’s vacuum piston modulates the metering rod’s rate of descent into the main jet. At high manifold vacuum, the vacuum piston restricts fuel flow through the main jet by pulling the 0.071” portion of the metering rod into the jet. As the throttle plate opens and intake vacuum is reduced, the metering rod spring pushes the metering rod vacuum piston upward, allowing more fuel to flow around the 0.047” portion of the metering rod’s diameter.

Effects of Manifold Design
Carburetors deliver fuel in the form of small droplets suspended in a moving column of air. After the fuel leaves the booster venturi, the droplets tend to reunite in the form of larger droplets. These fuel droplets also tend to fall to the floor of an intake manifold plenum and to flow around the outside circumference of a curved intake manifold port.

This process of fuel segregating from the air inside the intake manifold is generally known as “wet flow.”

Designers of street performance manifolds attempt to reduce wet flow by applying exhaust heat to the underside
photo 7: adjusting throttle plate perpendicular position in relation to the throttle body will prevent minor mixture distribution problems at wide-open throttle.
Photo 7: Adjusting throttle plate perpendicular position in relation to the throttle body will prevent minor mixture distribution problems at wide-open throttle.
of the intake plenum. Although this added exhaust heat tends to evaporate liquid fuel by heating the plenum floor, it also reduces the volume of the air stream entering the engine’s cylinders. This segregation process is further aggravated by intake ports that are too large for the application and intake ports that have unnecessarily sharp curves in the port wall.

Consequently, it’s important to remember that manifold design controls not only the total air flow into the engine, but the cylinder-to-cylinder fuel distribution as well.

External Adjustments
Most specified thermostatic choke adjustments are accurate at sea level. As operating altitude increases, tension on the thermostatic choke spring must be reduced to accommodate reduced atmospheric pressure. Both the choke spring tension and fast idle speeds should be adjusted on a cold engine in order to produce the best cold-engine driveability.

The idle mixture adjustment consists of lightly seating the two spring-loaded screws located at the base of the carburetor. After seating, the idle mixture screws should initially be adjusted by backing them out two or three turns from their seated position. In general, a tachometer should be used to adjust idle mixtures.

Photo 8: A common drill bit can be used to measure float height. Right and left float heights should be equal.
Photo 8: A common drill bit can be used to measure float height. Right and left float heights should be equal.
The idle speed screws should be adjusted equally until maximum idle speed is achieved. Keep in mind that, since performance carburetors can’t compensate for intake air temperature, a stoichiometric mixture in a hot shop environment will likely develop into a lean, rough idle condition in a cooler street environment.

A maximum idle speed adjustment will generally produce the best idle quality in a street environment. When adjusting idle mixture for minimum exhaust emissions, a slightly lean air/fuel mixture might be achieved by turning the idle mixture screws in to reduce engine speed by about 50 rpm. After the idle mixture is adjusted, the idle speed should be adjusted to specification. If the engine has a performance camshaft, the idle speed should be increased until an acceptable idle quality is achieved.

Most carburetor rebuild specifications indicate an accelerator pump height and linkage position adjustment. Lacking those specifications, adjust the accelerator pump by reducing pump stroke until a hesitation appears during acceleration. Increase pump stroke until the hesitation disappears. See Photo 6.

Last, always adjust the throttle linkage until the primary throttle plates achieve a wide-open, vertical position. After adjusting the throttle linkage, inspect the secondary throttle plates to ensure that they also reach a vertical position.

Keep in mind that partially opened throttle plates can cause poor cylinder-to-cylinder fuel distribution. Secondary throttle plate vertical position is adjusted at the secondary linkage. Most secondary plates also incorporate a throttle stop to ensure that the plates don’t rotate to an over-centered position. See Photo 7.

Internal Adjustments  
Float level dimensions are adjusted by gradually bending the float arm until the float level reaches the
specified dimension. See Photo 8.

In most cases, the float should align parallel to the float bowl cover surface. Float drop is adjusted by bending a limiting tab located on the float arm. On the model 1407 Edelbrock carburetor, the float should drop nearly to the bottom of the float bowl.

Primary and secondary main jetting is very close on a new Edelbrock carburetor. In most cases, the only adjustment required is reducing the main jet size one or two steps to compensate for higher altitudes.


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Holley Cab Tech 101
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The modern “square” design of Holley carburetors was popularly introduced during the late 1950s. Because this style of Holley carburetor featured a simple, modular design with interchangeable parts and a great degree of adjustability, it immediately found favor with performance enthusiasts. In this story, we’ll use the Holley 4150-series carburetors to illustrate how to select,

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assemble, adjust and diagnose most Holley carburetors for non-emissions performance and restoration applications.
See Photo l.

 

Before we start, it’s important to know that Holley carburetor “list” or identification numbers are found on the front of the choke tower or immediately behind the throttle linkage on racing carburetors manufactured with no choke towers. Keep in mind that the model number (4150, 4160, etc.) designates the carburetor configuration while the list number designates the actual design application.

Basic Metering Circuits
A Holley carburetor is made with four basic parts, the throttle plate, main body, metering block and float bowl assemblies. As with most domestically produced carburetors, a 4150 Holley has a choke, float, idle, off-idle, accelerator pump, air bleed, main metering and power-enrichment metering circuits.

Whether thermostatically or manually activated, the choke provides mixture enrichment for cold starting and cold driveability performance. Unlike many domestic carburetors, the 4150 Holley float assembly is externally adjustable. The accelerator pump is located under the float bowl and the accelerator pump passage extends through the metering block, main body and to the pump discharge

nozzle. The metering block contains the idle mixture adjustment screws and the idle, emulsion tube, main metering jet and power-enrichment circuits. The off-idle mixture passages, idle speed adjustment and secondary throttle linkage are located on the throttle plate body. The main body contains the idle bleeds, main metering air bleeds, booster venturis and the primary and secondary venturi vacuum ports for versions with vacuum-operated secondary throttle plates.

Selecting the Right CFM
Carburetors are rated in cubic feet per minute (cfm) of air flow at, for example, an intake manifold depression or vacuum of 1.5” Hg. To illustrate, a highly modified 350 cubic-inch displacement (cid) small block Chevrolet (SBC) engine that has achieved 100% volumetric efficiency might flow about 700 cfm of air at 7,000 rpm. A classic solid-lifter, “big-block” Chevy, Ford or Chrysler engine might flow about 780 cfm of air at 6,000 rpm.

Stock engines of the ’60s and ’70s normally ran at about 80-90% volumetric efficiency. A well-prepared muscle car engine of the era would operate at nearly 9% volumetric efficiency. A highly modified, naturally aspirated, open-exhaust racing engine might operate at 100% or more volumetric efficiency.

In all of the above cases, installing a larger cfm carburetor won’t increase horsepower because the engine spends 99% of its time operating below “redline” or peak operating speed. Installing a carburetor flowing slightly less than the peak requirements of the engine usually delivers better performance throughout the engine’s power band.

Secondary Applications
The “double-pumper” mechanical secondary throttle configuration uses a larger-volume, 50 cc accelerator pump and a sophisticated pump metering system to keep fuel flowing into the engine as the secondary throttle opens. If the engine can’t achieve enough air velocity through the secondary venturis, a temporary lean-out situation will develop after the accelerator pump stops injecting fuel into the air stream.

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Consequently, mechanical secondary configurations are recommended only for modified engines in vehicles of, for example, less than 3,400 pounds of weight and with numerical axle gear ratios of 3.90:1 or higher. In contrast, vacuum secondary configurations are recommended for heavier vehicles with mildly modified engines, heavier chassis weights, automatic transmissions and lower numerical axle ratios. A vacuum-operated secondary throttle is, in most cases, more desirable because a constant depression is maintained under the secondary throttle plates as the throttle opens.

 

The vacuum secondary responds to engine speed and load by receiving a vacuum signal from a small hole drilled into the apex of the primary venturi. See Photo 2.

A smaller hole may be also be drilled into the secondary venturi that helps open the secondary throttle plates once air begins to flow through the secondary throttle. Even with this level of engineering sophistication, many performance enthusiasts mistakenly believe that the driver should “feel” the secondary throttle open. Unfortunately, the desired “feel” is usually a momentary lean stumble caused by the secondary fuel metering catching up with secondary air flow.

Vacuum Chamber Assembly
When assembling the vacuum secondary chamber, form the

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diaphragm into an umbrella-shaped configuration, insert the diaphragm shaft into the lower part of the housing, then clamp the shaft in a vise to allow the chamber cover to be installed. See Photo 3. Many vacuum chambers contain a ball check that slows the opening of the secondary throttle. Although some drag racers leave the ball check out to speed up the opening of the secondary, the check ball configuration works well for most applications.

 

Holley offers a wide assortment of diaphragm springs that allow the secondary throttle opening to occur at different wide-open throttle (WOT) engine speeds. Optional housing covers are available that allow the springs to be changed without disassembling the carburetor. When assembled, the ability of the vacuum chamber to hold vacuum can be easily tested by depressing the diaphragm rod and then covering the vacuum port.

When testing, the secondary throttle shouldn’t open by merely “dry-revving” the engine in the shop. A better way to bench-test the vacuum secondary is to blow compressed air past the secondary vacuum port located in the primary venturi at WOT. The secondary throttle should open smoothly to a vertical position. Vacuum chamber operation can be tested on the vehicle by slipping a paper clip onto the diaphragm shaft and pushing it against the lower vacuum chamber housing. During a high-rpm acceleration test, the paper clip should be pulled down the length of the shaft when the secondary throttle opens. Last, Holley incorporates a throttle stop screw on the secondary throttle that prevents the throttle plates from sticking in the throttle bores. To adjust, turn the screw in until the screw firmly engages the secondary throttle stop.

 

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Adjusting The Accelerator Pump
The accelerator pump is operated by a lever that follows a plastic cam located on the throttle shaft. The accelerator pump discharge volume can be increased, changing the location of the mounting screw from #1 to #2 position. See Photo 4.

 

Accelerator pump cams on some carburetors might have three positions and adjust in the same manner. The pump lever spring travel must also be adjusted to allow 0.015” of clearance to exist between the pump spring adjusting screw and the pump diaphragm arm at WOT.

Holley also supplies a wide range of accelerator pump cam profiles that allow the pump discharge rate to be tailored to the engine. If the pump is initially adjusted to specification and a slight hesitation is noted during throttle tip-off, a slightly higher profile cam might be required. In addition, the pump discharge rate can be increased or decreased by changing the orifice size of the pump nozzle. Usually one step larger or smaller (0.003”) will indicate if the discharge rate can be improved.

Adjusting The Power Valve
The power valve numbering system indicates the level of intake manifold needed to close the power enrichment circuit. A #65 power valve, for example, will close at 6.5” Hg of intake manifold vacuum.

Although most 4150 carburetors use power valves ranging from #65 to #85, a “lighter” power valve (#45 or #55) might be required at extremely high altitudes or with highly modified engines that achieve relatively little intake manifold vacuum.

In general, if the power valve remains closed too late, a slight hesitation will be noticed during acceleration. If the power valve opens too soon, the engine will run rich during low-speed, part-throttle operating conditions. In most cases, the specified power valve should be used. Otherwise, the vacuum rating of the power valve should be one-half of the idle-speed vacuum reading. Automatic transmission readings should be taken with the engine idling and the transmission in gear.

Last, only Holley high fuel-volume, shielded-diaphragm configurations should be used in performance applications. The rectangular fuel outlet slots identify the high-volume power valve. The shielded valve reduces the probability of diaphragm damage from an engine backfire.

Adjusting The Float Level
When installing the adjustable float needle and seat

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assembly, always lubricate the assembly O-rings with engine oil and make sure that the float bowl bore is free of rust and scale. The initial float level is adjusted by holding the bowl upside down and adjusting the float needle until the float sits parallel with the top of the bowl. See Photo 5.

 

The sight hole in the side of the float bowl should be used for the final float adjustment. With the vehicle on a level shop floor, the correct float level is achieved when a few drops of fuel overflow the sight plug when the chassis is bumped. For fine-tuning, remember that one flat of the adjusting nut equals about 1/32” to 1/16” of fuel level.

Although the needle assemblies are manufactured in various diameters and materials, the 0.120” steel diameters are primarily intended for methanol racing fuels. The 0.110” diameter seat with a resilient tip is adequate for most 4150 models. Because float level and operation is very dependent upon fuel pressure, Holley supplies a very reliable adjustable fuel pressure regulator to meet the needs of its carburetors. The regulator should be adjusted using an accurate fuel pressure gauge with the engine running.

Fuel pressure should be regulated to between 5 and 6 psi for normal driving. Off-roading might require 4 psi while full-bore drag racing might require 6-8 psi. Too much fuel pressure tends to make the carb run rich at low speeds, while too little fuel pressure might cause the carb to run lean during high engine speeds and loads.

Holley mechanical and electric fuel pumps are designed to deliver the pressure and volume needed for performance use. Remember that an electric pump should be installed with the proper key-on, engine off, safety shut-off devices in place.

Carburetor Main Jets
Holley jets are numbered according to fuel flow. As a rule of thumb, 600 cfm series units use 60-series jets, 700 cfm series use 70-series jets and 800 cfm series use 80- series jets. Jetting for a classic 0-3310-1 780-cfm Holley carburetor, for example, is #72 for the primary venturi and #76 for the larger secondary venturi. The nearly identical 0-3310-2 uses a 134-21 metering plate in the secondary throttle, which means that the plate has a 0.040” idle feed and a 0.081” main metering restriction.

Original jetting configurations for specific list numbers are available at www.holley.com/TechService. Keep in mind that a mechanical carburetor doesn’t correct for barometric pressure, ambient air temperature and atmospheric humidity. While stock jetting is adequate for most applications, the main metering can be adjusted by increasing or decreasing the jet size in two-step increments. In general, reduce one jet size per 2,000’ increase in altitude and one jet size per 10° increase in ambient air temperature. On carbs with secondary metering plates, change the main metering restriction first.

Before determining the need for re-jetting any carburetor, always clean the primary and secondary air bleed jets first by using a light aerosol penetrant like WD-40. If a solvent is used, clean thoroughly and follow up with a penetrant. Next, make sure that the float level, fuel pressure and fuel pump volume are to specification. Last, if the carburetor cfm matches the requirements of the engine, jetting changes should seldom exceed three to four steps at sea level. The only exceptions to this general rule are racing engines using a lot of camshaft timing and running with a tuned open exhaust.

Diagnosing Holley Performance Issues
In general, most Holley carburetors may run rich due to an O-ring failure on the needle and seat assembly, a ruptured power valve or a failure of the main metering block gasket to seal correctly. If the float level adjustment doesn’t respond, the fuel pressure is excessive, the needle assembly O-ring isn’t sealing or the float needle isn’t seating correctly due to dirt contamination.

In most cases, the idle mixture should be close if the idle mixture screws are lightly seated and then backed out 1 to 1-1/2 turns. If the idle mixture is rich with the idle screws turned in, the power valve diaphragm might be leaking fuel into the air stream. If the engine seems to have idle mixture adjustment or mid-range fuel metering problems, the metering block gasket might be cracked or the main metering body gasket surface might be warped. For best sealing results, use the “blue” Holley metering and float bowl gaskets and don’t over-tighten the mounting screws.

Assembly Tips

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At the outset, the most common amateur mistake is to over-tighten the float bowl screws. Consequently, it’s important to check the main metering body for warpage when disassembled. A warped main body surface won’t allow the metering block to compress the metering block gasket evenly.

 

Mild cases of warpage around the mounting screw threads can be corrected by carefully filing the surface flat. See Photo 6.

More serious warpage might be corrected by tapping the corners of the main body surface down with a light hammer and then filing flat. This is a risky procedure, but the less attractive option is to replace the main body. When assembling the float bowl and metering block to the main body, always use snug the float bowl screws in an incremental and diagonal pattern until the gasket is seated. Remember also that the accelerator pump nozzle retaining screws also deserve a light touch because the threads in the metering body are grooved to allow fuel to flow around the nozzle retaining screw.

If the carburetor is installed on an open-plenum intake manifold, an aluminum four-hole “screw plate” should be installed under the carburetor to prevent loose throttle body screws from accidentally dropping into the engine. A similar 1/4” insulator gasket will also serve this purpose. Last, over-tightening the carb to the manifold mounting studs can break the throttle body casting at the accelerator pump arm pivot. A nut driver is the perfect tool for tightening Holley mounting nuts.

A Word About Custom Carbs
Many aftermarket companies specialize in customizing Holley carburetors to meet the exact requirements of any specified engine. Holley also provides 4150-series carburetors with adjustable air bleed and emulsion systems. Because these carburetors feature adjustable air bleed and emulsion tube systems, the initial setup must be accomplished by testing the carburetor on an engine dynamometer. Consequently, tuning of these types of carburetors is best left to professionals who have the data needed to achieve the “fuel curves” needed for maximum engine performance.




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