hi from a newbie - i mow about 5 acres with a Craftsman DGS 6500 with a Kohler 26 hp Courage model SV735S my question is i can be mowing just fine and all of a sudden the engine bogs down, smokes like i am trying to kill all the mosquitoes around the place for about 5 - 10 seconds, then clears up and everything is fine again. the engine has 615 hours on it. any help or suggestions would be greatly appreciated.