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1991CR250RBEAST

'99 YZ400F Smoking

3 posts in this topic

First, determine if it's smoke you see or steam. Steam will vanish into the air as it drifts away and cools off, smoke won't.

If it's steam, it's most likely a head gasket.

If it's smoke, and it smokes more under power than off the throttle, it's probably oil rings, which can be bad in spite of good compression rings. If it tends to smoke more when you first open the throttle after coasting down, but the smoke tends to stop if you leave the throttle open some, it's more likely valve guide seals.

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There is very little smoke while on the throttle but when it's idling it seems to smoke more. If it's been sitting for a day or so you would swear the world was on fire when I start it. My guess is oil seeping onto the Piston while sitting then when starting it burns up.I believe you hit the nail on the head.

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