Small Engines (Lawn Mowers, etc.): Kohler stops running, blown head gasket, rubber gasket

Question
I have a 6 1/4 HP Kohler Model K141T, Spec. No 29357d which is difficult to start but when it is started, it runs for about 5 to 10 minutes and then it seems the governor lever moves to shut down the carburetor killing the engine.  What's wrong? How to adjust carb? Where to find carb bowl rubber gasket? Fuel is clean, new spark plug, doesn't seem to be over-heating.  Thanks Paul.  

Answer
The gov is closing the throttle proabably because of an  ignition problem.  I'm guessing coil.  Is the spark blue or yellow?  If it's yellow go with a coil, if it's blue you proably need points and condensor.  As the points get old and wear down it causes ignition timing issues.

Another possible cause would be a blown head gasket.  When you crank the engine listen carefully.  Do you here a high pitched chirping sound.  If you do it is head gasket time.
The chirping is caused by the gasket acting like a reed in a saxophone.  If you have been to a 5th grade band concert it will help you know what sound you are looking for.