Motorcycle Repair: backfiring shadow 750, honda shadow 750, spark plug heat range

Question
cheers mate. i got an 83 honda shadow 750, came with some kind of aftermarket pipes to go onto it as the stock mufflers were rusted away. put them on, runs pretty good, set the carb floats and inspected all etc. changed the main jet to 120 from 118, intake stock still - runs pretty good but back-fires horribly on deceleration, and i mean horribly. also seems to run a little on the hot side, but not into the red or anything. i've opened the pilot screws a little more but doesn't seem to make much difference, plug isn't white but isn't brown either, light-grayish i guess. any help would be great - what is the common reason for back-firing? only on deceleration though, thanks and cheers, dennis.

Answer
Dennis,
the most common reason for backfiring
is changing to aftermarket pipes I believe.
Most of these pipes have less backpressure
and different design than original pipes. This allows fuel to get so lean it won't burn easily and so passes into
the exhaust pipe where it starts burning or backfiring.
Factors that contribute to this are:
-intake air leaks
-exhaust system leaks
-spark plug heat range too hot
-poor engine cooling
-lean fuel mixture
-bad air valve on carb
-idle set too low
-excessive carbon buildup
-vacuum hose leaks.
Try a cooler plug or raise carb
needles a notch.
Use your plug reading as a guide
to richen the fuel mixture.