Small Engines (Lawn Mowers, etc.): Kohler m18s, throttle position, crankcase

Question
I have a Gravely tractor (early 90s) with a Kohler m18s engine (Magnum 16). Everything was good till about a month ago. Engine began overheating and shutting down. Would always restart after cooling off. then It started pushing oil up thru breather pipe into carb. I pulled valve spring covers off and noticed that there was a lot of build up on back of valves and blow-by on right side of engine intake valve. so I decided to replace them, I also rebuilt carb. due to float valve not seating and causing fuel to flood into crankcase hence the oil blowing into carb due to crankcase being overfull. Now engine starts and runs great but it seems to overheats after about 45 minutes of run time, When it starts to die out, If I reduce throttle position to half way it keeps running longer. I double checked tapet clearance and all are in spec. Could it be possible that I did not get good enough seats on valves when I lapped them or am I looking in wrong direction?

Answer
Hi Jim,

A leaking exhaust valve would cause overheating at the exhaust but I can't see what would cause general engine overheating.  I suspect the shutting down is caused by a faulty ignition coil.  Check for spark when it shuts down.

Let me know what you find.
Michael