Small Engines (Lawn Mowers, etc.): kohler 20hp (m20 1999) surging, craftsman lawn tractor, vacuum lines

Question
My Craftsman lawn tractor has started to surge. I'll describe:1. Surges at high speed ,no load
                2. a load returns the motor to smooth operation
                3. at high speed,no load , pulling the choke out slightly smoothes the engine
                4. I' ve replaced the air filter , the fuel filter and the spark plugs.
                5. there is no loss of power at any speed.
                6.  the surging is becoming noticable at slower speeds.
     Help...thanks, Frank  

Answer
Almost all surging problems are carburetor related.  Check all the intake gaskets in the carb system for leakage.  If all the gaskets are sealing, then your next step is to remove, disassemble and clean the carb.  With the engine loaded the carb butterfly opens more and allows more fuel to enter the engine...that is why is does not surge when loaded.

Many technicians incorrectly diagnose a surging problem to be governor related...this is rarely the case unless someone has been tampering with the governor system.

Like I said, check the all the intake/carb gaskets, even vacuum lines.  If you do not find any leaks the I would clean the carb with compressed air and carburetor cleaner.

Let me know what you find.
Eric