I own and operate a kiot ck25 tractor. For 3 years it has run perfect. But after the last fueling, the engine will not go above 1600 rpm. The tractor starts good, The A-B lever is in nuetral, it runs good in idle, I have good hydraulics, I checked the fuses(all good), The tractor will drive in all gears good, but cant obviously gain speed because of the fact that it will not accelerate above 1600 rpm. I changed the fuel filter, checked all other fluids(all good) bleed the fuel system as per the operator manuel. I am at a dead end, and the snow is coming with plow jobs soon to be backed up. anyone with a possible solution? need help.