[Thodge]

If you are usually running your gas adjusting valve around 1/4 turn open, try opening it to half a turn or even more and see if the backfiring on acceleration stays the same or lessens. As stated above, the most common causes of backfiring through the carburetor are lean mixture or an intake valve stuck open. If making your mixture more rich helps, then you’re chasing a vacuum leak or fuel delivery problem and if it doesn’t then it’s probably a valve. Does the backfiring happen right as you open up the throttle on acceleration or does it start to happen during a sustained pull?