NOT REALLY. What does the spark plug look like, black and sooty, or white, or tan/brown? What did you do last time you ran the engine, Did you run the engine at high rpm, under almost full load? There's lots and lots of guys that don't realize the difference between "full load" and "high RPM". Your engine will run 3600 rpm with NO load, the throttle valve in the carb will be only about 1/4th the way open, maybe a bit less. When mowing tall grass it's easy to run high RPM and full load, Your Kohler will really be barking at you!
Best sign of a leaky head gasket is oil drewling out the front of the cylinder head and running down the cylinder fins just to the right of the exhaust port. Sanding/grinding the head FLAT will stop that leaking. I also recommend spray painting the new head gasket with Aluminum paint before installing and torquing it to specs in the correct order shown in the service manual. Install it before the paint dries.
The exhaust valve runs tremendously hot, under full load almost white hot, that's why the accumulated carbon has turned white. Less than full load the valve runs cooler, at idle it probably only gets 300-400 degrees F.