i have an 89 sportster 1200 when idle/rev breaks up backfires. If the choke is out and idling it dont do it much.
-rebuilt carb,changed plugs,plug wires,choke-check petcok
seems like gas flows little fast when i drained tank/and the overflow line is dripping gas
-before carb rebuild there was extra gas in carb and airfilter
- i am at a loss as to what could be the problem please help !
ps. ran great 3 days before then all the sudden started???

 

Do a search on adjusting your Air flow needle. Sounds like you need to adjust it. Maybe a little lean. Also check for exhaust and intake leaks since you had the carb off.

 

When you put the carb back on make sure you use some dish soap and water on the gasket. I did on the manifold and on the inside to the carb. just rub it on with your finger... less is more. Once it heats up makes for a nice seal.
I had a backfire problem on my 02 1200 I got last year, and I called my buddy and thats what he told me to do... worked. Runs like a clock

 

If the problem persists, then adjust try adjusting the carb. Forgot to put that in there.