Small Engines (Lawn Mowers, etc.): eingine backfires, john deere 212, valve adjustment

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The text above is a follow-up to ...

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The text above is a follow-up to ...

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I have a1990 john deere 212 riding mower with a 12hp koehler motor. When I first start it, the motor backfires thru the muffler. After it has been running for a couple minutes, it smooths out and runs fine. It only backfires when I let it set all night and start it up. Any advice you can givr me is appreciated. Thak You. Dale
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When was the last major tune-up including a valve adjustment and carb rebuild?

Let me know.
Eric
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Does the engine burn any oil?  When was the last major tune-up including a valve adjustment and carburetor overhaul?
Let me know.
Eric

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Are you having trouble with the website?  I receive your question but I need some more information to provide advise.

Does the engine burn any oil?  When was the last major tune-up including a valve adjustment and carburetor overhaul?

Let me know.
Eric