Is it poping out the carb or exaust. does it do this at all rpm's or certian spots. What are your points set at. have you checked the plugs and seen if it was running rich or lean, could be alot of things but missing and backfiring are usualy an easy fix, just something youve over looked.
i think the 68 will continue to work fine. that's what i'm running 295/68. when i got my bike it already had the s&s super e with 28/66. my plugs were very white, and it sneezed and popped into the carb when running no matter which way i adjusted it. moved up to these jets as per advice here and no more lean running. added lollipops and got rid of my mid range drag pipe stumble too, just in case that's been plaguing you.
The tank just came out of the package and I painted it...brand new high test gas...I was thinking the screen on the pingel should be sufficient but it really acted like dirty fuel yesterday when I rode it... it would "sputter" for awhile and then fix itself and run good...The only explanation I could think of is fuel contaminants ...
They usually say you should put tank sealer in new tanks. They often come with rust and welding scale inside them. Check the screen on the pingel and see what it looks like.
yes I would get copper core plug wires. They have always worked better with points for me, so it would be one variable gone out of the equation.
I have had a bad coil act for all the world like gas starvation before. Worth a check.
And +1 on check gas cap is venting right. Some lids are non vented, others vented. Must match the tank type.
In theory there is no difference between theory and practice. In practice there is.