Motorcycle Repair: 78 cb400 hondamatic, air fuel mixture, lean air

Question
My bike seems to run a little rough when cold even when choke is on.When warmed up will idle and run well.Noticed sometimes will misfire when idleing and backfire when revved up.Bike has 6100 miles on it and does this when warmed up only. Please help

Answer
Michael, the backfiring is typically an indication of a lean air fuel mixture.  On the side of the carbs, there's a roughly round shaped cover held on by two screws.   That is an idle air shutoff valve. When the engine is idling or decelerating, it shuts off the air to the idle circuit and keeps it from leaning out and backfiring.  It's pretty common for those to deteriorate and cause this kind of problem.

Regards
Rich