Sorry didn't answer the whole question the popping backfiring is caused by a combination of factors. 1) The sudden leaning when you shut off the gas and the engine is still turning higher revs than idle or forcing higher revs than the engine has fuel for (engine braking). 2) The introduction of fresh air into the exhaust, either through the AIS or an exhaust leak.
Opening the PMS softens this abrupt fuel transition and the removal of the AIS (only if you have no catalytic converters) will remove this air in an otherwise (no exhaust leaks) well running bike. Some will say one or the other works fine. I have found the combination of both these actions works best.
2005 1100 Custom
ORKed 5/16" Lines
PODs K&N RU-600s W/PCV
PCS XXX/2 cams
Jetted & PMS Tweaked 20.0/152.5 3.0 turns
Wimmer Machine Custom Oil Cooler & Stash Tube
Dyna 3000 Step 5/ 6500 redline
6" Fwd Control Extension W/Boards F&R
Memphis Shades Bullet Fairing
Progressive 465 rear
Progressive Springs and GVE front
10,000 Monkeys throwing crap at the glass and this one thinks he's Picasso...