tractor engine runs fine, until i engage the blades. then the engine starts to miss, sputter, and i think it would stall. (cant cut the lawn) then runs fine when i disengage the pto . have changed spark plug, air filter, gas. have also checked under deck for debris--seems clear----cleaned built up grass also. all belts fairly new and seem to work properly(not smoking).
i have posted this before---help!
Post the model information from the engine, as well as the model number of the mower, if possible. It sounds like you have ruled out the most obvious problems so we may need to start looking at the carb.
Lets start by removing the carb and giving it a good cleaning. Don't lose the jet in the bottom of the plastic center piece because it will fall out. The jet may be partially clogged if the engine is running lean when you engage the pto or the air bleed is clogged if running rich. Problem should be limited to the high speed side of the carb, which would be the jet, emulsion tube and air bleed jet which would be located at the entrance of the carb.
If that doesn't fix the problem, then lets go look at the valve clearance, and make sure there isn't one either not closing all the way, or maybe the cam lobe is worn and will not stay open long enough. If you turn the engine over by hand it would look like one valve opening 1/2 an inch, and the other opening 1/8 inch.
Fuel filter problem would start out fine, and then start running lean after a few seconds to a couple minutes. When an engine is running without load, even at 3600 rpm it is running on the idle jet of the carb. When you put a load on the engine, and it opens the throttle, then it will get fuel from the high speed jet. A partially clogged high speed jet will cause a lean run condition under load but will run fine at no load.
