Motorcycle Repair: 1980 650xs yamaha running on 1 cyclinder, dual fire, air cleaner

Question
Both cylinders have compression (120 PSI) Left cylinder works and right doesnt. We swapped plugs, wires, carbs. Coil dual fire only nothing had an effect.  Checked for valve sticking. Put different head on it. Has new ignition on it. We had a another motor in it did the same thing.

Thanks Vicky

Answer
first thanks for usind All experts to answer yor  question.
 you mentioned you changed or swapped all these parts ,first check for fire to that paricular cylinder if you have fire and compression ,then all u need is fuel for combustion to happen in the cylinder. take off air cleaner to that cylinders carb, start motorcycle,  spray some carb cleaner into intake side of carb if bike idles up u have a fuel problem.this should give you the insight to take care of the problem. good luck and keep ridin

                       mitch