1999 YZ 250 Fouling Plugs - Jetting Questions

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

 

Need more info, what average throttle position are you doing when the plug fouls ?

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

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.

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.

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.

Between 180 and 230 Psi IMO

Between 180 and 230 Psi IMO

Thanks

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

Sounds like a bad ignition coil or spark plug wire.

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