bought a yz125 1987. it runs fine until it warms up then it dies. I built the whole top end new gaskets. adjusted the power valves. reeds are good. packing in the exhaust in silencer is good. what else could it be??
easy answer is the crank seals. They need to be replaced every 10 years or so. Gasoline with alcohol content can make them last less than 1 year. Old seals aren't made to handle the drying effect of alcohol. Be aware.
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