Hi all, I have an Exmark lazer hp with a kohler 23 hp with 150 hours. It is now loosing power under load. Seems to idle ok but when I hit the grass some black smoke comes out and it start sputtering. I changed the spark plugs and air filters but this didn't solve problem. I did notice that it had too much oil in it and I drained out about half a quart to get it to the right level....could this have caused damage? My next thing to try is to change the fuel filter. I have run a tank of carb cleaner through it. I wonder if the ethanl log grade gas here in NY is causing the problem? Any thoughts? thanks!