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


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

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.


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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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