This is the first time ive had a top cylinder go wrong. This is also the first time ive had a prob with a 250. Its normaly the 300 that kicks me.

I ended up taking the crank out and flushing the cases. The piston didnt fail i dont think. What has happened is both sides of the barrel above each exhaust port have broken up. Taking out about 10mm square. You can now see light above the power valve even with them lifted to the open pos.
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If I have to take the carbs off once more...