Motorcycle Repair: miss, carbuerators, honda 400

Question
I see you prefer specific Hondas, but perhaps I can imposed you to ask a pretty general question about a 1980 Honda 400 carbureted twin that misses at idle and at constant speed, but accelerates and runs well otherwise.  Plugs have been changed with no difference. Minor backfire when decelerating.  Aside question, do you know what the two wings on the bottoms of the carbuerators do?  They turn stop to stop about 250 degrees but don't seem to do much if anything?  Thanks

Answer
One of the fuel/air circuits is blocked in one of your carburettors.  From your description it sounds like the idle/slow running jet.  You will need to take the carbs apart to clean that out; usually this is the smallest jet in the carb, which is why it clogs first.  If you want to identify it, let the bike idle and find out which exhaust stays cold.  Good luck,  Jan