Small Engines (Lawn Mowers, etc.): Mower engine surging

Question
The 23 hp kawasaki engine on my zero turn mower started surging when in a no load state. It seems to run ok when it's turning the wheels or moving the blades. The surging will stop if the choke is advanced about halfway. The engine has only 62 hours on it. The air filter is new and the governor appears to be functional and I've used only non ethanol gasoline in it. I would think that a clogged fuel filter or pump would also effect the engine in a load state - probably in the carb, but was hoping that it might be something less involved. Can you steer me in the right direction on this problem ? Thanks, Leenw

Answer
There are 2 circuits in almost all mower carbs; a high speed when the engine is under load and a low speed for normal running.

The circuits are controlled by the position of the butterfly shaft and holes drilled in the carb ventri.  

When you turn the blades on the governor system moves the carburetor butterfly and the high speed circuit delivers extra fuel to the engine.

I suspect the engine is running lean in the low speed circuit since the choke affects the surging.

I'd start my removing, dis-assembling and cleaning the carb with compressed air from an air compressor and use some spray can carb cleaner.

Today's carbs are precisely tuned for EPA requirements and can be very sensitive to any blockage.  Honda's are probably the most sensitive followed by Kawasaki.  Most of the time when I dis-assemble I never seen anything in the carb.  The compressed air must blow some of the little carb hole clean as most carbs usually work fine after cleaning.  I recently had a Briggs carb with light green build-up in the carb.  I soaked and cleaned the carb but it still surged.  Ended up replacing for $50.00 and it runs perfect.  My guess is the light green build-up was preventing the fuel from properly being delivered.

Eric