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02 yz250 fouling plugs and other issues

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Hey guys i just bought a yz 250 and im having problems with fouling plugs. It starts first kick idles fine has tons of power but after ive been riding for a while and i stop and let it idle and then try to go again it fouls the plug. Possible right crank seal? I've already tried 2 sizes leaner on the main jet. Had a 175, put a 170 in it. Same thing. As soon as i put a new plug in it starts on the first kick. The fouled plugs are always completely soaked.

Another issue is the brakes. Mainly the front brake. Lever has a good feel doesnt feel spongy but it just wont stop the bike. I have to use my whole hand to use it effectively. Im used to a one or two finger front brake like my '12 crf250. Pads look almost new... Tusk typhoon oversize rotor kit??

Yet another issue is the rear shock feels very springy (bouncy) and feels like the whole bike rolls back onto the rear wheel under power. Is that a job for Factory Connection?

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First off, the fouled plugs could be any number of reasons, but is probably jetting related. But a leak down test is the only sure way of knowing whether or not the crank seal is leaking oil. You can build a leak down test cheaply, and test your engine. There's a thread here, search for it.

 

A weak front brake that is not "spongy", is usually associated with a contaminated disc & pads. Usually caused by a leaking fork oil seal that leaked onto the disc & coated the brake pads rendering them useless. Spray brake cleaner on the disc and scrub it with a scouring pad, and replace the pads, and your front brake should return to normal. It still won't be as strong as the Honda ones, manufacturing differences, but it will be one/two finger usable.

 

And your rear shock sounds "blown". It needs to be rebuilt with fresh oil & a full charge of Nitrogen by someone reputable, like Factory Connection, etc..

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First off, the fouled plugs could be any number of reasons, but is probably jetting related. But a leak down test is the only sure way of knowing whether or not the crank seal is leaking oil. You can build a leak down test cheaply, and test your engine. There's a thread here, search for it.

A weak front brake that is not "spongy", is usually associated with a contaminated disc & pads. Usually caused by a leaking fork oil seal that leaked onto the disc & coated the brake pads rendering them useless. Spray brake cleaner on the disc and scrub it with a scouring pad, and replace the pads, and your front brake should return to normal. It still won't be as strong as the Honda ones, manufacturing differences, but it will be one/two finger usable.

And your rear shock sounds "blown". It needs to be rebuilt with fresh oil & a full charge of Nitrogen by someone reputable, like Factory Connection, etc..

Thanks for the info Maniac. By the way i have an older wr400 parts bike. Could i put the WR shock on it and change out the spring? They look almost identical..

Now that i think of it, he said he just replaced the fork seals so im sure thats why the front brake is so poor. (Brake pads off the wr??)

As for the for the plug fouling, is it uncommon for them to burn trans oil if the right crank seal is bad?

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I'm not sure on the exact overall length, but almost all current Yamaha shocks can be switched between models. There will be valving differences, and spring differences, but they almost always will bolt up.

 

Same with the brake pads. There almost all the same mounting, so they should fit.

 

If your right side crank seal is leaking, then your engine will burn oil and foul plugs. A leak down test will determine if it's leaking. And if it is, it has to be fixed.

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Figured out the plug fouling problem. Previous owner had turned the air screw all the way in and then turned the idle screw way up to make it idle. I put the 175 jet back in it. Seem like it could possibly be running a tad lean. Maybe i'll raise the needle one notch. At least im not fouling plugs now. Got fork seals ordered along with a bunch of new plastic and Attack graphics. Also got silencer packing, x ring chain, grips, new exhaust springs and seals and a bolt kit. I'll have less than a grand in it when im done.

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Sounds like the pilot circuit is rich, not the main jet

 

 

Yes you are correct. The air screw was turned all the way in and the idle turned up to compensate. I got it pretty well sorted out but i cant really test it because the forks are apart at the moment getting new seals. How do you set the air screw on this bike? I know how to set the fuel screw on a four stroke not sure about the 2 strokes

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Starting position is 2 turns out from a lightly seated "all the way in" position. Then with the correct sized pilot jet, the air screw should be anywhere from 1 turn out to 2 1/2 turns out,  to achieve the best low end performance, or "snap" off idle.
 

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