Hi All, firstly Im new but been surfing here for awhile now. I think there is a lot of good info here, so here goes. About a year ago I bought a Kohler Courage Pro (SV600) 20 hp single cylinder for my "hobby" unit. The tractor is a Simplicity 16 gth. The Kohler was a repower as the briggs was shot. Anyway I got the motor on the tractor and all wired up with not too much problem. Then I went out to mow my acre yard. Well then I ran over the muffler that had fallen off the front of the motor, cuz I forgot to tighten it down. So that humbling experience brings us up to now. When I am trying to run the tractor sometimes it will run just fine for a little while and sometimes it will do this thing from the very start. What it does is, well it just sounds like a car with the timing set wrong. The motor falls all over itself and there is no power and there is a kind of clanging, thats the best that I can describe the sound that I hear. Also there has been fuel blowing out of the carb on the air cleaner side when this happens. I have had the head off and no marks on the piston from the valves. And I reset the valves "loose". I have checked the fuel pump and put in new fuel filters. I have also taken the carb apart and checked the float level. The motor was new but used when I bought it. So unless you all can come up with something I am just about ready to take this to the shop but would really rather not. So any ideas guys? and thanks.