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 !

 

If choking it helps then it could be an air leak. I'd check that first. Too much fuel in the carb & air cleaner can be a float setting too high. Big cams can also cause this. Look at the carb when it's idling & see if it blows back & forth. This will cause fuel to puddle in the carb & air cleaner. Pulling the choke can stop it. What kind of carb is on it?

 

where should i check for an air leak? iv already checked for one on the intake. float is calibrated right. Could it be a vacuum problem? no holes or anything in it. It has the stock cv carb.

 

Having he same problem, what was the fix?

 

This is an old thread. But, if you can rule out air leaks at the intake gasket and exhaust ports, I would check for a torn diaphragm in the carb.