Motorcycle Repair: 78 hondamatic 400, air fuel mixture, speed jets

Question
Thanks for the clue on the air cut offs but I replaced them and it did not remedy the problem.It seems to not idle up and run without your hand on the throttle when the choke is on until it warms up then after that is when it wants to backfire when you throttle up or get off the throttle.Is there somthing else i should check? Could the carbs be out of sinc?I have tried to adjust the small black knob which i think is an idle adjustment between the carbs at the bottom of carbs but that only makes it backfire worse when raising the idle.

Answer
Michael, the backfiring is caused by a lean mixture.  The idle air shut off valves are supposed to keep the fuel from going into the cylinder when you decelerate.  Have you checked the low speed jets? If those are partially plugged or if the float level is too low, it could cause this problem.  You are looking for something that is leaning out the air fuel mixture.

Regards
Rich