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)
Does anyone know what this could be?
Thanks for your help in advanced.