I have a 2011 exmark laser z with the Kaw FX801v engine with 825 hrs. I am having a similar problem with mine. One mechanic said the valve clearance may be off. I too checked the same things such as air filter, new spark plugs, fuel filter, gas cap vent and it made no difference. I dropped it off at the local shop to check the valve clearance. Please post if you get it resolved. I'll do the same.