At Holley Performance Products, we're always looking
for ways to help our customers help themselves. Through
the years, we've developed a number of manuals,
newsletters, and videos for do-it-yourselfers. Soon
these will be available through an online Customer
Service Center. Here, we have asked our technicians
to provide answers to frequently asked questions.
Got a question? We have the answer.



Top Questions & Answers

QUESTION How do I find the "list" number on my carburetor?

ANSWER The list number for most performance and factory 2 and 4 barrel carburetors will be found stamped into the upper right hand corner of the airhorn or sometimes called the choke tower. On the 4150 HP models that do not have a choke tower the list number will be stamped into the mainbody behind the throttle linkage. This number is used to identify the carburetor and also used when needing service parts or renew kits.

QUESTION How do I adjust the fuel level on my carburetor?

ANSWER Setting the fuel level should be the first thing you do before attempting to make any further adjustments.The float level should put the fuel level just below the bottom of sight plug hole. You will make the adjustment with the vehicle on a level surface and the engine idling. You will first remove the sight plug, then to make your adjustment you will need to loosen the lock screw on the needle and seat. This will allow you to turn the adjusting nut to raise or lower the float level. Each hex flat on the nut will change the float level approximatly 1/32". When you have the fuel level just below sight plug hole you will then tighten the lock screw and reinstall the sight hole plug. Make sure you have a shop towel handy in case you have any fuel leaks from the Sight plug or needle and seat adjusting nut.


QUESTION I have a camshaft with a long duration and a high lift. It will burn your eyes at a idle. What can I do to fix this?

ANSWER The most common cause is an improperly rated power valve. You will first need to choose the correct power valve for your application. This is covered in another section of the Technical Information Library. When you have a camshaft of this configuration it requires more air and fuel for it to operate efficiently. This in turn requires you to raise your curb idle screw to obtain the same given rpm that you had with a stock camshaft. If you are having a problem with the air/fuel mixture screws not making a difference then what happens is with turning the curb idle screw in farther this will sometimes cause the throttle plates to open too far and they will uncover the idle slots. This will allow it to bypass the idle circuit and start pulling fuel from the transfer slot. To correct this problem you can raise the secondary throttle plates a little with the secondary adjusting screw allowing more airflow into the engine. This will allow you to lower the primary throttle plates so you will be able to get back into the idle circuit. Another method would be to drill a 1/64" - 1/8" hole in each of the primary throttle plates on the side closest to the transfer slot. This will allow extra airflow into the carburetor also alowing you lower the primary throttle plates.


QUESTION My vehicle has a stumble from a dead stop. What can I do to cure this?

ANSWER The most common cause of a stumble is not having an adequate accelerator pump shot. The first thing to do is to look at the discharge nozzle and make sure you are getting a good strong pump shot. If not then you need to inspect the pump diaphram for a hole or tear. You will also need to make sure that the pump passage is clear from any trash or debris. First you will need to check the adjustment on the pump. To do this you will open the throttle all the way (WOT). Push the pump arm lever down and then adjust the pump override spring to obtain .015" clearance between the pump arm and lever. If you are having a stumble and no black smoke out the tailpipe then you will need to increase the shooter size. If it stumbles and you are getting black smoke from the tailpipe then it will be nessasary to decrease the shooter size.


QUESTION I have a vacuum secondary carburetor that bogs when the secondaries come in. What will cause this?

ANSWER Bogging and hesitation are caused by the secondaries coming in to quickly. You can install a heavier secondary spring and this will prevent the secondary from coming in to soon. If the engine is sluggish in response at full throttle then the secondaries may not be opening soon enough. You will then need to go to a lighter spring.


QUESTION I can rev the engine when it is in park and the secondaries will not open. Why is this?

ANSWER The secondaries will not open by free revving the engine. The engine needs to be under a load before they will open. If you are still uncertain if they are opening or not you can take a normal paperclip and clip it onto the secondary diaphram rod. You will then push it up against the bottom of the secondary diaphram housing, now you will need to go out and drive the vehicle. When you return you will be able to look at the position of the paperclip on the rod. If it is lower on the rod then you can tell the secondaries opened and how far they opened. This is useful in determining if you need a heavier or lighter secondary spring.


QUESTION How do I know if a vacuum or mechanical carburetor is best for me?

ANSWER For streetcars the vacuum secondary carburetor works best on midweight or heavyweight cars with an automatic transmission. They are more forgiving than a double pumper is because they work by sensing engine load. The mechanical secondary carburetor is best on a lighter car with radical camshaft and a lower gear and manual transmission or on a car that is going to be used for racing purposes.


QUESTION After I shut my car off and come back out the next morning there is gas on the throttle shaft and puddled on the intake. What causes this?

ANSWER This is usually caused by percolation. This is when the engine is shut off and the engine temperature rises it causes the fuel to boil in the bowl and leak out of the boosters. There are a couple of things you can do to cure this one is make sure the fuel level is not too high. You can also lower the fuel level about 1/8" below the sight plug hole and this will cure it sometimes. The heat from the engine will rise into the carburetor sometimes and will cause the fuel to boil. Installing a phenolic heat spacer between the carburetor and the intake or a heat shield can cure this. These parts will prevent heat from getting to the carburetor and boiling the fuel.


QUESTION I just bought a new carburetor and it has a warning that it will not work with an overdrive transmission. What can I do about this?

ANSWER This warning was placed with the carburetor because if not installed properly with the correct transmission kickdown bracket for the GM 700R4 it will result in premature transmission failure. Part #20-95 and the kickdown mounting stud part #20-40 will allow the proper adjustment of the cable.


QUESTION How do I find my local Holley dealer?

ANSWER You can locate your nearest dealer by calling the dealer hotline at 1-800-2HOLLEY (1-800-246-5539).


QUESTION Can I buy directly from Holley?

ANSWER We do not sell direct to the public. All sales and warranty returns are handled through your Holley dealer.