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KX250F New Piston making backfiring?

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I just had my KX250F piston replaced and now it backfires constantly. I called the guy who replaced it and he said it's normal. He said it will stop once the engine/piston is broken in. Does anyone know if this is should be happening?

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BS. When does it backfire? I'd bet during deceleration. If so you probably have a loose header pipe or something that is causing an air leak.

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Yup, total BS.

He just doesn´t want to have another look at it.

Check header and copper crush washer first.

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either exhaust leak or lean jettting, the only other possiblilty is that you got your hands on a vintage Orville Redenbacher piston :p

sorry couldn't resist

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I just had my KX250F piston replaced and now it backfires constantly. I called the guy who replaced it and he said it's normal. He said it will stop once the engine/piston is broken in. Does anyone know if this is should be happening?

have u noticed if it has ever done it before the top end rebuild?

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My vote would also be a leak at the exhaust header or somewhere along the pipe. Check where the exhaust header goes into the cylinder, and also check or replace the copper crush gasket.

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If it is backfiring during acceleration, I would definitely have a look at the timing.

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