Question about 2003 Yamaha YZ 250

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1988 yz 250 ,lacking power,spitting oil,possibly power valve?

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More than likely the majority of the problem is related to poor compression pressure. When was the last time the engine was re-built (a new top end)?

I would suggest evaluating the condition of the piston, ring and cylinder. Replacing the piston and ring and won't set you back much if the bore in the cylinder is good and it will definately perk your bike back up.

Clean that air filter too - a plugged filter will cause the bike to run rich, too.

Posted on Jan 13, 2010

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Try repacking the silencer first

Posted on Oct 22, 2012

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If you are spitting oil out the pipe then most likely you have an internal seal leak. The gear oil is separated from the crankcase by a seal to keep the gear oil and the 2-cycle gas-oil mixture separated. If the seal is leaking then the gear oil is entering the combustion chamber on the exhaust stroke and pushing it out the tailpipe. I bet you are also fouling out the spark plugs pretty fast due to this.

Posted on Jan 21, 2010

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