# Bone white exhaust valve



## justin3 (Apr 10, 2007)

Hey everyone,

Im working on a 12hp vertical shaft Briggs and Stratton engine off an MTD rider. The engine had was run with a carb that overflowed constantly and had a clogged low mixture jet. While the engine was running I could sometimes see small sparks shoot out the exhaust muffler and I feared the engine was burning up. I disassembled the head and found an almost perfect bore with the piston nice and tight in the cylinder and no real damage that I could see. The only thing I noticed was that the exhaust valve was bone white. What would a bone white exhaust valve mean? Does that have anything to do with the sparks I saw coming out of the exhaust? If not what would cause the sparks? 

Thanks everyone and heres a picture to help.


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## 30yearTech (Sep 14, 2006)

If you were to run most any small engine in subdued lighting, you would probably notice sparks coming from the exhaust. Thats one reason that spark arrestors are required on all small engines used on federal properties. Sparks are generally caused by small heated flecks of carbon. Since the mufflers on many small engines are mounted very close if not directly to the exhaust, there is little time for any cooling of the exhaust gas before it exists the muffler.

From the look of the engine in your picture it appears pretty much normal to me. I would not expect the exhaust to look this way if it had been running with a flooding carburetor though.


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## justin3 (Apr 10, 2007)

Thanks again 30year, I see what your saying about the sparks, it makes sense because my muffler is in bad condition and probably has nothing left of the spark arrester. I ordered a gasket kit and new exhaust valve because the other one had a bit of a groove on the lip.


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