i have a mid 1990s vintage hopper, 25hp kohler command pro, about 800 hours. Have had it for about 7 years. Recently it labors badly when encountering a stretch of thick grass to the point I must disengage the pto before it dies. Once it reaches this condition, it will barely cut. And must go very very slowly if at all. My theory is somethings gets hot and binds in the drive train. I’ve replaced the gearbox in the deck as well as one set of bearings on one of the three spindles in the 60inch deck. I’ve also replaced the coils, new plugs, new fuel filter, new belts, air filter is clean, belt tensioners appear good, blades move freely, clean gasoline, ok compression I think of 135&155psi. usually if the mower sits for a day or two it will run good for any period... 20minutes or an hour until thick grass is encountered. By process of elimination I can only think of replacing the remaining spindle bearing and the drive shaft bearings. Any other ideas?. This mower usually goes through anything, it’s a beast.
Look into carburetor accelerator pump. It is supposed to squirt extra gas into throat if governor throws throttle open. If it is plugged or even partially plugged, that would cause what you describe. A dirty air filter would cause it too. Governor malfunction can cause it too. Some governors are belt driven, and belt tension on those types is critical to prper performance.
#3
Hammermechanicman
You replaced the coils. Have you double checked that you have spark at both coils? Big twins can run well in one cylinder till engine is put under a heavy load. Do both spark plugs look the same after a few gours of mowing? A bad bearing won't wait for a heavy load before it seizes. Have you checked for a leaking head gasket?
