I bought an 03 vtx1300r. I've had the bike for two years now and done routine maintenance. The pipes are stock but when I had bought the previous owner did the Clayton mod. The bike has always done a backfire/popping upon decel in second. Now it is sounding like I am shooting a cannon out of the pipes at cruising speeds. Not upon accelarating just holding constant. I thought maybe it was the spark plugs and changed them again. This had no affect positive or negative. I asked my local dealership and they told me to rid myself of the problem I'd need to purchase new pipes, a jet kit, and a better air system. I don't know if they just want to make some serious money off me or if that will end this issue. Any help with this would be greatly appreciated. Also is it harmful to the engine in any way?