If it did it before you changed mufflers & installed the fueler that rules them out, no ex. leaks don't leave much, possable it's the injection system? I've gotten harley' tech support to warranty a MAGNETTI MARELLI, flipped me out because it was 9 years old. The systems are subject to wear and is not totally rebuild able. My tech tried replacing everything in the system and nothing helped, bolted on new injection unit and ran like a top. Could not get a smooth idle, and would get some poping while ridding. If you had a download you should not of needed a fueler, is there a chance the download was wrong to begin with? Pumping too much fuel to the cylinders in the decel part of the map causing the extra fuel to unite in the ex. system causing the poping? Just food for thought.