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Accelerator pump tuning

hunt2elk

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Been messing around fine tuning my Quick Fuel 750 mech. sec. carb and am down to the accelerator pump squirters and cams. My question is if you have your 4 corner idle mixture screws all backed out the same amount, and both idle speed screws are fairly equal, then it would make sense that both primary and secondary squirters and cams should be of the same value, correct? Cant seem to find any info anywhere talking about this.
 
try a holley tuning book. I will check mine and see if they mention squirters and cams
 
just checked my holley book and on page 127 it covers accelerator pump tuning
 
I've always believed it depends on what the engine wants for the driving conditions...and everone's behaves different. My 850 mech. demon came stock with pink cams on both, but I would get a short hesitation when flooring it from cruise rpm. I'm settled in with a blue cam on the primary and green on the secondary, with a 31 squirter in front and a 35 out back...it runs great like this, no bogs/hesitations etc. Try different things one change at a time, you'll find the sweet spot for your setup. Books/charts/friends' similar setups can definitely help you make educated guesses to get started in the right direction. Ultimately for best results you want to tailor things to your specific setup..it takes time but that's the fun stuff! Good luck!
 
just checked my holley book and on page 127 it covers accelerator pump tuning
Which book are you referring to? I have David Vizards 'Super Tune and Modify Holley Carburetors', and while it does talk about adjusting the pumps, it really doesn't go into depth on the subject.
 
I've always believed it depends on what the engine wants for the driving conditions...and everone's behaves different. My 850 mech. demon came stock with pink cams on both, but I would get a short hesitation when flooring it from cruise rpm. I'm settled in with a blue cam on the primary and green on the secondary, with a 31 squirter in front and a 35 out back...it runs great like this, no bogs/hesitations etc. Try different things one change at a time, you'll find the sweet spot for your setup. Books/charts/friends' similar setups can definitely help you make educated guesses to get started in the right direction. Ultimately for best results you want to tailor things to your specific setup..it takes time but that's the fun stuff! Good luck!
Sounds like I have a similar issue to what you had. Mine is lazy from idle-1500 until 2500rpm when flooring it. I will try what you did just for the heck of it today. What I am struggling with is I don't know if my symptom should be addressed on the primary or secondary side? I do enjoy making adjustments to try to get it the best it can be, but I have been fighting this engine for 2 years now. Right now it is the best it has ever been. My biggest problem was a bad distributor, but once I chucked that in the trash things are slowly progressing.....
 
Lazy?? Is it bogging? I ask because lazy sounds more like timing. I fought with my curve for quite awhile before I got it right, mines very lazy if it isn't idling at 30 degrees.
 
lazy/flat (no spitting or popping thru the carb) is too much fuel.
 
Lazy?? Is it bogging? I ask because lazy sounds more like timing. I fought with my curve for quite awhile before I got it right, mines very lazy if it isn't idling at 30 degrees.
No, not bogging at all. I would love to run more initial timing, but can't because of hard starting when hot. The bad distributor was from Don and I spent 2 summers dealing with him on that. This motor just doesn't make enough vacuum to run hooked up like yours.
 
lazy/flat (no spitting or popping thru the carb) is too much fuel.
So do you think I should try going from 80 to 78 secondary jets to see if that leans out the wot a bit?
 
No, not bogging at all. I would love to run more initial timing, but can't because of hard starting when hot. The bad distributor was from Don and I spent 2 summers dealing with him on that. This motor just doesn't make enough vacuum to run hooked up like yours.
I'm no timing genius but I'd think all the carb tuning in the world wouldn't wake it up if the initial isn't where it needs to be? How do the drag guys get around not having enough vacuum... do they just deal with the hard cranking?
 
I'm no timing genius but I'd think all the carb tuning in the world wouldn't wake it up if the initial isn't where it needs to be? How do the drag guys get around not having enough vacuum... do they just deal with the hard cranking?
I think most run theirs locked at 35 or whatever they want, but then have the ignition wired up to get the motor spinning, then flip a switch to let the spark come through.
 
The most important thing to do that no one has addressed is the acc. pump adjustment.
You have to open the throttle fully and then also push the acc. lever all the way down and measure between it and the acc. arm. You need to have a minimal space between the two at this point. I always use .008. Holley wants to make sure that you have some gap here so as to not rip the acc. diaphragm. I see so many people don't know to do this and there is like 1/4" of slack there which will cause a major bog. It helps to make a tool to hold throttle open or to have a helper. If this isn't right your wasting your time changing squirters and cams. This has to be done each time you move or change a cam.
Ron
 
the book is HOLLEY CARBURETORS & MANIFOLDS by mike urich & bill fisher( HP books)
 
holley 1.png
hope u can read
 
Thanks NOSTRT980, LOL. I'll get a copy of that one ordered.
 
At what point should a person consider going to a 50cc acc. pump on the secondary? Assuming timing and advance curve is right. Trying to get the big bog out at under 2000 rpm( 4 speed) And I can't get enough gas through the mechanical secondaries to make black exhaust smoke. ........................MO
 
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