How To Adjust The Accelerator Pump On Holley Carburetors

How-to adjust the accelerator pump on Holley carburetors to avoid stumbling and hesitation upon acceleration. Tips include: How to check for the clearance between the accelerator pump diaphragm arm & operating lever; how-to select the correct accelerator pump nozzle size, and accelerator pump cam selection and installation. Additional information can be found on Holley’s website:



17 thoughts on “How To Adjust The Accelerator Pump On Holley Carburetors

  1. I have a 340 with a 6pak on it. Took it to a performance shop to get the carbs tuned. Well when i got the car home. I cranked it to get it off the trailer and fire comes out the carbs. Dude screwed my car up and now i cant find the info to tune out the carbs correctly. I know he screwed on the accelerator pump which this shows me how to reset it. Any more links on Holley carbs to figure the rest out would be greatly appreciated. Im sure i will be needing some nozzle changes as well. It (3)500 cfm sitting on a small block. So they need to be tuned down. But even at idle i can smell it rich. It idles with only 500 cfm. Any video links to adjust air fuel at idle?

  2. Ive learned more about the correct operation of carbs watching these two holley videos than all the mucking about for 20 years getting things to run almost perfect.. Now I cant wait to apply these principles to other carbs.. Excellently explained!

  3. I dont have 500 spare carb parts laying around. This should not be as difficult as you make it. Seems like you have to adjust by trial and error by swapping out part after part to get it right which means it could be weeks by the time you get the carb running right with having to wait on shipping each time you try a part and it doesnt work.

  4. Thank you for a very thorough and detailed coverage of this subject. This information was hard for me to find. I've subscribed and will be back. These carbs have lots of adjustments, that can be both good and bad. Having a good understanding of them puts one well on the road of squeezing out all the performance they are capable of. Thanks again.

  5. good video and very informative. I'm new to this and never worked on carbs but I have 2 cars and 1 truck that have carbs .currently having problems with one and I think it's time for me to learn. this video definitely was helpful , one of the best explained I've seen so far.

  6. That'snice, but useless for older Holley carbs, such as my 2280. It would be nice if you included the years covered in the video title, though a lot of uploaders don't care about hionesty, because they want more views. This is NOT "How To Adjust The Accelerator Pump On Holley Carburetors", it's, "How To Adjust The Accelerator Pump On Some Newer Holley Carburetors". Back I go, to look for info that actually applies to my carburetor!!!

  7. If the secondary diaphragm is damaged this could affect how the secondaries open if they open at all. If the idle mixture screws are set too rich it could be loading up with fuel and not burning completely. I tune to highest vacuum on the idle circuit. Idle screws only affect the Idle circuit ive come across some ppl who think it tunes the carb throughout the throttle range. You also want the vacuum advance attached to the ported side, not full vacuum port on the carb.

  8. Hope you got it figured out over the past year. If not it could be a timing issue. Your timing could be advancing too quickly or your timing is too advanced and could be advancing more than it should when the mechanical and/or vacuum advance kicks in.

  9. If my pump is delivering too much fuel, It would only have a momentary effect right? I.E. It should actually bog down when I apply full throttle? What would it mean if you get "run on" when using full throttle? If I apply more than 3/4 throttle, then go to shift, my RPM's actually spike for a second during the gear change, despite having my foot off the gas for that moment. I thought it was my accel.pump but now I'm thinking I was wrong….

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