It shouldn't pop with a bang. It should gurgle. Some mild popping on decel is normal. You are either lean or have atmosphere rentering the head from the exhaust.
Need some more info, too:
Is the AI still on the bike? If yes, get rid of it cuz that is the problem. It introduces air back into the system and make it lean.
What size pilot jet? Did you and John change it?
If it was turned correctly, (I'm sure it was if John was there) then you likely have a leak in the exhaust. Did you use exhaust sealant when you put the TOR slip-on's on?
the first three things to check before tossing the TOR's (TOR's aren't that loud on the exhaust DB scale):
1. Use hi-temp RTV sealant on the TOR slip-on joint. Problem still persist? Goto #2
2. Check torque at header to head bolts. these are known to loosen up.Problem still persist? Goto #3
3. Check the mix screws. Turn one all the way and count the revolutions to get your starting point. Should be 2.5 turns or something like that. Start turning the mixture screws out 1/4 turn at a time(both of them, of course) and go for a test ride. This richens up the mixture. If you get to 3.5 turns, you may need to step up a jet size or two (assuming you are still at the stock 40).
