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cr250 2001 fowling plugs please help

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If the engine has ever run clean in the past always with the same :

jetting, premix type and ratio, ambiant temperature.


and only now is suddenly starting the foul plugs,  you could suspect :


-worn / loose carburetor components that allow extra un-metered fuel (needle's jet orifice worn oval shaped)

-carburetor float / fuel level is set too high, inlet needle and seat not sealing properly (higher fuel level richens all circuits)

-worn or damaged intake reeds, despite still looking good they are a wear item as they loose tension with usage

-worn or damaged right hand side crank seal, allows gearbox oil into the crankcase (level been dropping lately?)

-weak ignition system

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Mlatour nailed it. It's going to be one of those things...  I have a 2001 bike with the Keihin PWK carb swap done. I replaced my spark plug the last time I did the top end.. I only replaced it as part of a normal top end.. The old plug was still good. That was OVER 2 YEARS ago. Your plug should not be fowling in 4 hours.

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