Motorcycle Repair: cb 750 backfires on downshift, lean mixture, cb 750

Question
have a 73 with 76 cb750engine has pod airfilters yoshi repro 4 to 1 dyno ign idles good accelerates fine but when i let off throttle it backfires timing seems like it doesnt advance enough when accelerating, never reaches full advance mark, is this normal? and are these problems related?  thanks richard

Answer
Sorry for the delayed response, I've been out in the yard burying a drain pipe. Richard, they are not related.  The backfiring is from a lean mixture on the idle air adjustment.  If you turn the screws in a little, it will richen up the mixture.

The full advancing problem is not unusual.  It's more important to get full timing advance rather than have the right advance at idle.  Go ahead and advance the timing until you reach the furthest timing advance mark when the bike is revved up.

Regards
Rich