QuestionI have a 1979 honda cb650, and it really bogs after it warms up. I have found
that when the bike is first started and the choke is pulled all the way out, the
bike launches a lot better. I have just gone through the carbs, and cleaned
the idle jets as good as I can, but since they are pressed in, they are really
hard to get clean. I set the pilot screw to 2 twists, .5 less than recommended
since I am running this bike at 5000 ft. I assume that I am running a lean
mixture at idle, and some adjustments need to be made. Do you think that I
should clean the jet needle and throttle valve? But I have been told that you
should never need to take that part of the carb apart. Do you think that I am
diagnosing this problem correctly, any comments are greatly appreciated.
Thanks a lot
AnswerJonathan, Should be richer, rather than leaner at that altitude. If the engine runs better with choke partially on, when warm at part throttle, then you have probable air leaks or lean mixture condition.
If the bike will idle smoothly with your 2 turns out setting, then you got the idle circuits cleaned.
Sounds like the transition to part-throttle is where you are having issues. Look for carb synchronization problems, air leaks at the manifolds/air box connectors. If the air filter or exhaust has been changed from OEM, then you will have jetting issues, in many cases.
The needle condition should be fairly apparent and can be cleaned without removal.
Something that can greatly affect carburetion is compression and ignition timing. This series of engines has two small spark units, back by the battery, which can cause problems. Be sure that your spark is strong on all cylinders. If you have weak spark or intermittent spark, then check wiring connectors and condition of spark units. If they look overheated, they could be failing.
All of this assumes that you have a fully functional charging system and a fully charged battery.
Bill Silver
