Mower has a 20 hp Kohler motor, is 13 years old, and very well maintained. New deck assembly this year. Teenage son runs mower out of gas. He puts gas in but it won't start. I assumed it may have sucked up some trash when it ran out of gas. I got it running again by changing the fuel filter, pulling the carb and cleaning it out, and new plugs and air filter. Mower runs great, as always. However, now, when I engage the blades, the motor sputters and will die if I don't disengage the blades. I don't believe this mower had a safety switch other than the one under the seat that shuts down the blades if no weight in the seat. Kind of feels like electrical, but how would I check that? If it were fuel, would it run so well the instant I disengage the blades? Thank you for any help you can offer.

Two possible things here. The grounding on the seat may be bad which in turn will cause the mower to shut down in the blades are engaged. Jump a safety switch to test it.

Also just because it runs with no load doesn't mean the air fuel mixture is correct on the carb. If its to lean then it will stall on a load quick...

Is the carbs linkage correct and free in movement??