QuestionBill,
i have been an auto & truck mech. for thirty years and a racer all of my life, but this is my first motorcycle. its a 72 cb350 twin w/2,000 miles - been in dry storage since '74 - i have cleared up all fuel delivery problems by disassembling petcock & carbs and cleaning them in hydroseal tank - have installed new battery and new plugs - points - condenser (oem honda parts) the thing now starts immediately and you can balance the carbs w/the idle speed screws to idle smooth at 1,000 rpm. the problem now is that if you take it out and run up through the gears it willthen be idling at 3,500 - 4,000 rpm - you must back off the idle speed screws to get it to idle down - then set base idle again. also, the idle mixture screws have very little effect on how the bike runs.
AnswerButch.... motorcycles are just minature cars... the same rules apply.
Bikes with high idle problems, generally stem from worn or sticking spark advancers, located behind the points plate.
If the springs are stretched or the cam is gummed up and sticking on the shaft, then it will advance the spark timing, which raises the engine idle speed.
I will assume that your carb diaphragms are all okay and the intake manifold connections are tight and the rubber is not excessively cracked. There is a gasket between the manifold and the cylinder head, so you might want to renew that item to cut down on any intake air leaks.
Do check the throttle cable for kinks and sticking issues, too, as well as the throttle drum assembly for any hanging up issues. Be sure that the cable is routed so it doesn't get pulled when the handlebars are swung to one side or the other..
Bill Silver
