I read alot of post and tried alot of ideas on this probleme. Still i havent fixed the probleme. The car starts fine, idles fine, and even drives around fine. But if you floor it you get a stumble and a backfire through the carb. I can ease into the gas and it will be fine. With me easing into the gas at a drag strip i managed a 14.4 @ 99mph. I would love to go WOT out of the gate. I checked timeing, made sure i was reading off TDC. I am running @ 14* initial and 36* total. I have a 350 bored .060 over. Vortec heads milled and ported with LS1/6 springs to accomadate a .550 lift. I have the voodoo 268 cam (227/233@.050, .489/.504), Edelbrock RPM air gap intake, MSD 6al, msd super conductor wires, MSD streetfire dist/cap/rotor. I have a 750 Speed demon w/ vac sec. and elec. choke feeding it. If i could get some more ideas on what i could do or how to tune it so it can stop doing that, that would be great. I have a race coming up this sat. against a guy at work with 4th gen camaro and i would really like to beat him so im begging you fellow TGO'ers to help me out.

 

Thats your accelerator pump not squirting enough fuel upon acceleration. The squirter might be clogged or faulty. You can also upgrade to a bigger booster pump if you have a holley. Also changing the accelerator pump plastic cam can help you tune it better.
The backfire on acceleration is definetly a lean condition on accel.
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I forgot. I also had a friend with a built mustang which did the same. I tried everything until I realized the little poping would not go away on accel. So we checked everything and found that he had a broken intake valve spring and it would only pop on acceleration. Pull the valve covers and check all the springs.
Hope that helps.

 

Thank you sir, i will try. Any ideas on what pump cam or is it just more trial and error type of deal? Should it stay squirting or just throw a big shot in all at once? Sorry for being such a noob.