If you’re backfiring through the carb - it may need to be inspected - especially a Holley. I agree - check for slipped timing first. Triple check the plug firing order and that the distributor cap is on correctly and the spark has an easy path. Ensure the polarity and gap of dist. pickup is correct - also check the coils polarity - positive is always 12v hot in crank/run - no interruptions. That the ecu is grounded properly and you have a nice strong battery or two.
Did you change all those parts because of this problem?
