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1999 YZ 250 Fouling Plugs - Jetting Questions

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We are located in Oregon and are trying to tune in this 1999 YZ 250 we just got, it is stock with a FMF Silencer.

 

Couple issues and its like clock work, it fouls a spark plug every 7-8 miles it would foul a spark plug. The jetting does not seam to be way off. What are people running for the air/screw , pilot jet, needle setting, and main jet?

 

Also in fifth gear it does what seams like the opposite of what would be a fouling a plug issue. It acts like it is running out of fuel and needs more fuel when in fifth gear. 

 

Any help would be greatly appreciated!

 

Thanks in advance

 

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Probably mostly half throttle stuff, it is in the trails., but also had an issue when wide open in 5th gear..

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Do you know the condition of the top end ? Reason i'm asking is you bike is a '99  an a tell tale sign of a worn out top end is plug fouling. I strongly recommend you first do a compression test before you start altering jetting.

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My plugs kept fouling too. After cleaning them up like new they would foul even faster. Then I decided to check the gap. I was using a nkg iridium core DR8eix(I think) untouched it was gapped at .719 instead of the recommended 0.5-0.6. I gaped it to .519 and it ran like it had a new plug. To gap a plug use a feeler guage.

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Do you know the condition of the top end ? Reason i'm asking is you bike is a '99 an a tell tale sign of a worn out top end is plug fouling. I strongly recommend you first do a compression test before you start altering jetting.

just curious, what psi should I look for when checking compression. 09 yz 250 all stock.

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Did the adjustment you made on the plug make a hotter spark??

Guess there is to many variables still.

Does anyone know anything about the crank seal issue that can cause different things to happen

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