I have a 750 holley with vacume secondaries. I put on a Proform main body and medering plate. Runs great except when at dead stop and stomp on it it will hesitate or fall on it face. If I ease into it it take off great. Also I noticed at any speed the inital step on the gas it will have a very slite hesitation but only for a millisecond and she is fine. I have had this problem even when I had the orginalcarb with the main body with the horn on a different motor. The new motor with the new main body and it still does it. My idle mixture screws are OK and I have the correct power valve, idles great and timing is right on. Any Help Thanks JOHN

first thing to check is the accel pump...look down the carb with the engine off and move the throttle,,you should see the accell pump squirt fuel as you open the throttle...if you dont see fuel coming out of the accell pump nozzle it can be a couple of different things..ie pump adjustment,accell cam, or the wrong gaskets..another thing to check is the vacumn to your distributor advance...is it manifold or ported vacumn?...manifold vacumn will retard on accell and ported will advance...
Steve

I have been working on the very same problem. I replaced the squirters (larger) and pump shot cam from pink to green. My setup has improved a lot.
Good luck.

I had the same problem with the same carb on my 406. I did not try diff. pump cams but I had to go from a #31 accell. pump discharge nozzle to a # 37( tried a #35 first and no help) Got rid of the flat spot off idle with the 37. It was suggested to me though that I should not have had to go that big if I would have tried diff. pump cam profiles. So I don't know which is the best way to go? But this worked for me. What size discharge nozzle is in there now? If you want a
#35 or # 37 I wil give you one because I have extras as they come in packs of 2 and I don't have a double pumper.

I had a hesitation on my Holley as well. Fixed it without changing cams or nozzles just by making sure the accelerator pump was set up properly. It has to start delivering fuel as soon as the throttle starts to open. I was playing with the 0.015" clearance, and just went until I had clearance when the throttle was off, but the second the throttle moved off idle, I'd get the shot.

Try this first - it's cheaper (nothing to buy) and might save you some gas money. If you're sure it's set up properly and you've still got a bog, then larger nozzles and different cams might be where you have to go.

JMHO
Wes

Thanks for all the help but if you change the cams out how do you know which one you should try next? I have all the sizes but not sure which design will work better? I have 35 in now but when I went to 37 ran terrible. I set my acc pump at .0015 with the throttle wide open and with diff varation but still hesitated. Help!

Well now can you tell if you are getting a bog or a lean out. If it got worse when you put the bigger squirter in , I am guessing that you are getting too much fuel comming off idle. Mine was definetly too lean as it is was backfiring when punched from idle. Yours may me getting too much of a shot and bogging. My 750 holley had a #31 squirter from the factory, maybe you need to go down a bit or are you sure that it is leaning out?