86w/76 engine backfires through carb

just swapped in a 76 350 4 bolt main minus emmissions with-edelbrock cam, carb, and intake; remanufactured crank; holley fuel pump; complete gasket set; starter; flywheel; cap, rotor, plugs,and wires. starts and runs perfect in park. but when driving lack of power and every once in a while it backfires up through the carb. have tried: different carb, dist, checked and rechecked timing.

old engine did the same thing. everything on new engine is new or different part. is their anything not related to the engine that could cause this.

could the brake booster cause this? it's the only thing hooked up from the old setup.

any vacuum leak could do that so check everything with a vacuum line. are you running the stock 86 exhaust? the cat might be plugged

checked vaccum lines with vacum gauge. everything thats not connected is plugged at the carb. The exhaust isn't stock-no cat's.

when it's shut off if you unhook the brake booster line at the booster does it suck in air? if not you probably have a leaky booster or bad checkvalve. did you try plugging the brake booster hose?

going to try that today or tom. working 10 hr days suck. I'll let you know what I find out. Thanks for the reply.