I have a Gravely 260Z with a 25 HP Kawasaki. The problem is when the mower is running without blades engaged runs great. After engaging blades and putting it under a load it bogs terribly to the point of shutting off. It doen't miss or spit and sputter just loses power. I have exhausted everything from replacing all filters, cleaning carb.,changing all belts, hoses in both tanks, adjusting valves.