QuestionHey Bill, thanks in advance for reading my question.
I have a 79 Honda CX500, It idles great, but just off idle the left cylinder leans waay out, and fires 1 out of 20 times, then backfires loudly (Most times thru exhaust rarely thru carb) If I choke that cylinder it runs much better. Ive cleaned carbs many times, they look nice. I did a vacuum test on it... the gauge jumps from 5-15 lbs, where the good running side is only 2-12. Checked the intake elbow, and checked the Air cutoff valve and it looks nice, even switched it from the other carb. Checked float levels, and they are both full right up to the bowl gasket. Ignition is working great, sparks every time, new plugs, even switched coils.
Checked fuel supply, and it flows very nicely. Im running out of options.. any other ideas? These are the KEI-HIN carbs.
AnswerMike, get a timing light on the engine, checking each side separately. This can be messy if you don't have the special screw in window tool, though.
Usually what happens with CX500s is that one of the pulser coils and/or the CDI control module has lost one side of the timing control. So, what happens is that one side gets spark advance and the other side stays fairly fixed timing at idle spec. This causes the variance in vacuum signals from side to side and confuses the metering circuits in the carburetors.
Go here, too: http://www.elsham.pwp.blueyonder.co.uk/cx500/wontgo/
for more help from the owner's group.
Bill Silver
