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So I am helping out my neighbor with her lawnmower, tuning it up and what not for the summer. I noticed that when running the lawnmower, as soon as you take it off of choke, it revs up as fast as it will go and stays there, no matter where the throttle is at. I decided the carburetor butterfly must be stuck, so I took the carb off to clean it. However, the butterfly wasn't stuck at all. As I was reinstalling it, I noticed what appeared to be a second butterfly valve inside the engine. What throws me off though is there is no way for this "valve" to rotate. As far as I can tell it is stuck there. Also, it is right before the piston in the engine and the edges appear to be beat up, which would mean it could not have been a factory part. (I think)

second valve in lawnmower?

Does anyone know what this could be?

Thanks for your help in advanced.

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It appears that the engine ingested something it should not have, and it got stuck there, as evidenced by the beat up edges. It may not be magnetic, but I would try to get a parts grabber or a magnet on it and see if you can pull it out. Getting it out, if it is unconnected, may help the engine run better. Also, you will be able to see further in, as perhaps this valve came off a shaft that is obscured by it presently.

Tape on a stick, chopsticks and other things may be fashioned to help you out. Let us know what you discover.

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  • You were right. After double checking the engine diagrams I realized it was the throttle value that had come loose and gotten stuck. Thanks for your help! – Megastrik3 May 6 '20 at 23:00
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It appears that the engine ingested something it should not have, and it got stuck there, as evidenced by the beat up edges. It may not be magnetic, but I would try to get a parts grabber or a magnet on it and see if you can pull it out. Getting it out, if it is unconnected, may help the engine run better. Also, you will be able to see further in, as perhaps this valve came off a shaft that is obscured by it presently.

You may find that you have found the throttle, unattached to a throttle shaft.

Tape on a stick, chopsticks and other things may be fashioned to help you out. Let us know what you discover.

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  • Non-magnetic, try a stiff wire with a hooked tip. – blacksmith37 May 6 '20 at 21:24

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