Got spark, lost compression...

[Mudrig150 331]

So I went to run my briggs 8 horse and of course it's losing compression out the intake valve. I pull the head and clean the literal chunks of carbon out and clean the valves. Instead of fixing the compression, cleaning the head actually made the intake seat worse. I must've dislodged carbon that was acting as a seal, because I found the entire valve seat scratched. There was tons of carbon near the valves, and some in the intake and exhaust. Guess that valve's been leaking for a while, and now I need to lap them. I don't want to do it, but at least I'll be able to pull the valves and clean the crap off the bottoms of them.

[stevasaurus 23,281]

Why are you getting all that carbon??  Running rich??? 

[The Tuul Crib 7,339]

Bad gas as well?

[Mudrig150 331]

I don't know. When I found it there was nothing at all in the tank. No rust or fuel. We've had the engine for a while but I don't know the history. I think it might be running rich, but not sure. The carbon is only on half of the piston, surprisingly, and on both of the valves, so, unlike my cub cadet which burned incredibly rich and I think was burning oil and was filthy, it is good.

Edited April 17, 2019 by Mudrig150

[oliver2-44 10,738]

If you have carbon on half the piston, that's a sign that you possible have "blow by" past the rings occurring. 

 

There is a possibility the cylinder is worn out of round,. lapping the valves may help extend the engines life a little longer, but an engine rebuild is in the future.

[Mudrig150 331]

The piston is well within spec. It's all around the valves where the spark plug is.