This has been addressed in a number of posts. A well tuned V twin will pop back on decel due to unburned gases in the exhaust. The factory pipes are so restrictive the pops are barely noticeable. Do a search as there was a link to a very good article explaining the phenomenon and why trying to eradicate it is counter productive. I've owned a number of V twin bikes from Harleys to sportbikes and learned to love the sweet burble of the pipes when decelerating. It's part of the V Twin song.