John, I imagine the bike only backfires when you decelerating and off the throttle ? ? ? And then not overly loud ? ? ? If the answer to my questions is yes, the problem is caused by the PAIR valve on the left side of the engine. Perfectly normal for this bike. Only way to stop it is to remove the PAIR valve. I can provide more information or check out www.volusiariders.com and do a search for "PAIR valve removal".