Motorcycle Repair: Higher Idle, cb honda, timing advance

Question
i have '78 CB Honda,23k mi. the problem is that the idle increases as the engine warms up. after a nice cruise and i stop and idle, it goes from 1000rpm to 13-1400. throttle is back all the way. otherwise it runs great, i can hear the lifters at idle though. timing advance issue or more serious? no smoke, tiny miss, starts on 1 revolution, could have lost a little power. i would love some advice from a vintage expert. thank you

Answer
RPMs going from 1k to 1.3k is not too bad. Basically the mixture is a touch lean on idle and as the bike warms up it runs more efficiently (warm engine needs less fuel). You can adjust the idle mixture fuel screws by turning them out a little bit (1/4 turn). This should increase the RPM slightly and then use the RPM throttle adjustment to set the RPM back down to 1k or so.

It's possible your carbs may need some cleaning. If you notice exhaust smells when it warms up that means it might be a tad rich. Also check the color of the spark plugs to make sure they are burning cleanly. They should have a light tan color.

It's common for the valves to make noise of these bikes. I believe your bike has solid lifters so you may need to re-shim them or adjust them (if they have the screw lock adjusters). I would refer to the service manual for this task.