Yz250 trouble please help

I was out riding yesterday, I had been riding on and off for about 2 hours then somthing went wrong. I was in 3rd gear and then i shifted to 4th and when I hit the throttle it felt like the bike lost power. So I pulled in the clutch and rolled to a stop and as I slowed down the bike started revving really high all by itself. So I hit the kill switch and after about 5 secs it finally died. Never had this happen before and I didn't like the way it sounded, if anybody has an idea please help thanks

Kinda sounds like you ran out of gas.

When it goes lean it revs up for a bit, then dies.

I'd say you have a crank seal leaking. When you have a seal leak, it allows the motor to draw air in and it will rev uncontrolled.

If the bike was not smoking excessively, the bad seal is probably on the ignition side.

You can change this seal without splitting the cases. You will need a puller to pull the rotor though.

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