Motorcycle Repair: idle revving, float bowls, air leaks

Question
1981 kawasaki csr 305- at idle it will rev up HIGH
on its own and then suddenly the rpm's will drop
mostly after giving it some throttle i mean the rpm will stay high after letting up on the throttle. bike runs ok down the road. one cylinder
is getting hotter than the other  

     thanks for any help!
                gary

Answer
Gary, the things that make bikes go into fast idle are air leaks in the intake tract and ignition timing and spark advancer problems. I think this bike still has points, so have the spark advancer checked first (behind the point plate) and then accurately set the point gap (after you clean them and lubricate the point cam), then set the point opening alignment with the F mark on the flywheel on both sides. Once you KNOW that the ignition timing is correct, then you can address the carburetors and air leaks at the manifold or any vacuum hoses. Some bikes have a vacuum operated petcock that can give an air leak, as well as reduce the fuel flow to the carburetors at the same time!
Be sure that the carb float bowls are clean and all the jets are clear, then the carb synchronization needs checking. These bikes were jetted really lean from the factory and hardly run when they are cold. Either raise the needle in the slide with some tiny washers and/or put a larger main jet in it to richen it up a bit.

Bill Silver