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Engine maintenance

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Just thought I'd post a comment about something you might want to do on your engine for maintenance.

I have had an A/C 716H for about eleven years now. Ever since I picked it up, it knocks when loaded really hard (tall dense grass, tiller fully buried, engaging the mower deck quickly). When it started knocking, black smoke would puff out of the muffler.

Figuring it couldn't go on like this forever without blowing up, I finally pulled the cylinder head off and had a look. There wasn't a lot of carbon build up, but there was a nice ridge of it around both valves. I cleaned all the carbon off carefully, put the head back on with a new head gasket and richened up the carb about 1/4 turn. The knocking has been resolved! I think the carbon along with having the carb just a touch too lean was the problem.

It's possible the noise was either preignition or detonation. I'm guessing preignition.

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