Jerry,
Back when I first got my Speedy, I bought Bub Megaphones. At first there was this horrible popping on deceleration (just as you describe). The biggest change came when I removed the A.I. system (air injection). Then, when I installed "the Freak," and put in the supplied 160 main jets, that also helped. Now it purrs.
My setup now is as follows,
Pipes = Staintune-Slashcuts
Filters = K&N's
Airbox = Removed (The Freak)
AI system = Removed
Mainjets = 160's
Pilot Jets = Stock
Air screws = 3 turns out
Needle shims = 1 - .020 shim on each needle
With that, it runs close to perfect (my elevation is about 200 ft. above sea-level).
-BT
