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I have a Zongshen 200gy-2 bike, that has of late developed a misfire if there is no throttle, like waiting at traffic lights.

It has recently been serviced, but the spark plug has not been replaced. The mechanic's comment was, "checked and cleaned spark plug"

Acceleration or high revs there is no misfire.

Any suggestions at to what can be the cause?

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2 Answers 2

up vote 3 down vote accepted

If the bike has a carburetor, try cleaning the idle jet (well, just spray the whole intake throat with carburetor cleaner, it's in there somewhere). If it's injected, then run a bottle of fuel system cleaner through it.

You might also have a problem with a dirty air filter, but if the bike was just serviced I assume they would have checked that.

You could also checked and clean all your ignition-related electrical connections, possibly when your generator output drops at low revs there's enough corrosion-induced resistance to affect your spark.

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It turned out to be the air fuel mixture, fiddling with the little adjustment screw on the carburettor sorted out the problems. –  Rihan Meij Mar 29 '12 at 8:12

Have you tried slightly raising the idle speed?

Often as engines age they become less stable at idle, generally through wear, so it can be worth tweaking the idle speed upwards a little to see if it solves your problem.

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