oil seal on the crank

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Nov 21, 1999
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#1
How hard is it to change the oil seal on the clutch side of the crankshaft? The bike is aYamaha yz 250 1998. I keep leaning out the jetting and it's still fouling plug's. I think it that seal? THe plug is black and wet. Any opion's are alway's appreciated. Thanks
 

HLT

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Dec 15, 2000
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#2
Clutch side crank seal

Jim, It's easy. Remove clutch assy. Remove drive gear and the collar behind it and the seal is well exposed. Rather than pry it out, you are better off to hook something small behind it and pull it out. To install the new one, you will need a socket or something that matches the diameter of the seal and can reach over the crankshaft. Tap in slowly and be sure to get the seal flush and straight. Put a small film of oil on the collar before you reinstall it so you won't damage new seal. Be sure to torque the nut on the crank properly. Reassemble the clutch, button it up with a new gasket, and go ride. One thing yoiu might check before changing the seal is the float height in the carb. If it's too high, it will cause a rich condition that jetting may not fix. Good Luck and have fun.
 
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#3
Thanks HLT, I didn't think of the float height. THe more I think about it that might be the problem. I'm getting cold plug fouling . When I change plug it's very wet, not so much oily but wet. I'll give that a try. I'll give you my jetting changes. Main went from 172 to 168, Pilot stock 48 went to 42. praticed Wednesday night, fouled aplug at the beginning. New plug , bike ran great all night. Thursday washed the bike, started it after washing, fouled a plug.I dropped the neddle one groove, but haven't tried that yet. Any opion's are appreciated.
 
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#4
Ok well here’s one. Check the float valve (valve attached/controlled by the float) & turn off the gas when not in use if you don’t already.

There may be petrol slowly (or maybe rapidly) leaking past that valve into the bottom end & when you kick start the bike it throws it onto the plug. Pudduck! Once fouled a plug often doesn’t recover so new is only option.
 
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#5
Dave thanks for the reply, I always turn the gas off when not in use. Took the carb apart yesterday. The float was off a little bit and there seemed to be a small piece of dried gasket sealer on the float needle. I'm not sure if it was there all along or on my hands. But everything is clean and hopefully right now. I have to wait till Wednesday night to find out.