Small Engines (Lawn Mowers, etc.): over heating, greasy dirt, head gasket

Question
I bought a snapper with a 25h kohler command motor off my uncle. It heat's the muffler up to the point that in the dark it glow's red.I replaced the head gasket's and my uncle replaced the muffler i guess about the time it started doing this but it  seem's to flow ok.the valves move freely and the motor hold's 155pounds compresion.thank you for any advise.

Answer
WOW!!  Have you checked the flywheel fins?  Is the engine dirty and greasy?  Dirt and crime on the engine acts as an insulator holding in the heat.  We dis-assemble most of the engines sheet metal and power wash the engine block when we do tune-ups...this  helps the engines run cooler.

What oil, brand and weight are you using?

Let me know.
Eric