I just put my 402 back in the 70 Chevelle after sitting 2 years waiting for body work. The carb is a holley Street Avenger 80770. I can't get the motor to not back fire through the carb. The only work to the motor was a new airgap intake and a new M&H engine harness for HEI.Car ran great before the down time. Checked and ajusted timing, change plugs and still backfires on acceleration. Could the carb be the trouble?

Lean pop. Ran into that one time turned out to be vacum leak.

It could be the accelerator pump dried out of plugged up a bit, that will cause a pop.

Dave

I replaced the accelerator pump when I noticed gas leaking on the intake. Thought I had it made.

Chris

Where is the timing at?

The last check was at 12 with the advance unhooked. Is is possible that the timing is still to far advanced? It seems the more I retard the more I have to turn the idle up.
Chris

I replaced the accelerator pump when I noticed gas leaking on the intake. Thought I had it made.

Chris
Did you adjust it for proper actuation after you replaced the diaphragm?

Did you install a new check valve (probably a rubber umbrella) in the bowl?

Chris, try 16-18* initial for testing purposes, then go after the carb if that doesnt cure it.

Yes, the more you retard the timing the more you have to screw the idle screw in.

Look for this simple fix- most carb backfires are caused by either timing/ distributor off a tooth, or a plug wire on the wrong cylinder, a crossed wire.

Look for this simple fix- most carb backfires are caused by either timing/ distributor off a tooth, or a plug wire on the wrong cylinder, a crossed wire.

Ditto, you did change the intake. I bet the timing is off or dist is off a tooth.

I will look thing over again. I know the distributer in timed right. Did it a couple of times. I just read another post about vacume advance. Does the cowl hood tee off the vac advance? Could this affect the timing? Thanks for the input. Let you know how I make out.

Chris