QuestionI have a 77 honda CB 550 super sport that I have build from the ground up. It runs and looks great, however I have a problem with the idle. On first start it runs great, after it gets warm the idle tends to die and I have to turn the idle screw to keep it going, this progresses as I ride. Another twist is when I hit the freeway and rap out aroung 5-6 thousand RPM, when I come to a stop the idle wants to race upwards of 7,000. I turn down the idle screw and can get it under control, but it seems to want to idle all over the place. I have completely rebuild the carbs soaked in carb cleaner completely apart, bench balanced prior to putting them back on, put in new jets, adjusted float bowls to specs and have new throttle cables. I am lost and can't get this thing to set. On the open road it has plenty of power and runs great. Any ideas?
AnswerScott, you may have one or more conditions that are affecting the idle.
Air leaks at the intake manifold, either at the rubber junctions or the o-rings at the cylinder head.
http://www.cmsnl.com/honda-cb550f2-super-sport-550-four-1977-usa_model468/partsl #7 and #15
Worn/sticking spark advancer, which won't return or advance cleanly. Remove the points plate and check the condition of the spark advancer. Clean and lubricate the point cam, both where it pivots on the advancer base and for the point rubbing blocks, themselves.
Use an dynamic automotive timing light to verify the spark timing at idle and at full advance.
I am finding that today's gasoline makes these old bikes run lean, so you might need to richen up the jetting one step to make it run even better.
Do a valve adjustment and check compression, too, so you know that you have a sound engine to work with.
Bill Silver
