QuestionI have an 'ol CB500T that I have been riding for a while & has started to backfire upon excceleration , only does this on the left cyl.I did clean & gap the points . everything looks fine there. I did notice that there is a bigger spark on the left set than the right . The backfireing is getting very "LOUD" what's the prob man?
AnswerWaylon..... Backfiring on acceleration, usually through the carbs (not exhaust) is related to a lean condition. The left carb has a small diaphragm, designed to prevent backfiring on deceleration. When the diaphragm fails, then you have a massive air leak instead. Check BikeBandit site for illustrations. If that is not the case, then verify valve clearances, compression and timing for both sides. Watch the points while the engine is idling. IF there is severe arcing across one set, then the condenser is failing or lead is loose/disconnected.
Last thing to check would be some kind of blockage to the fuel supply/metering. Water in the float bowl, float level incorrectly set or blocked passages/jets.
FYI, Point gap should be about .014" on both sides, then set backing plates to provide point opening right at the F and LF timing mark alignments. Be sure that the spark advancer is working properly, before you finalize the timing, though. You will have to remove the point plate to access the spark advancer.
Bill Silver
