The 28 HP Kawasaki motor on my Exmark has been having issues for several months now and they seem to be getting worse. I took it too my dealer and they of course blamed it on ethanol in the gas and all of that sort of thing. Even though it's only had maybe 3 or 4 gallons of gas with ethanol ran in it and that was 2 years ago. I'm not sure what they did to it, but it ran a little bitter for about 4 hours worth of mowing and now it's sputtering and missing worse than before. It almost seems as if the motor is starving for fuel or something. I've done the obvious stuff such as new plugs and fuel filter but that hasn't seemed to help. What I have noticed is that when I turn the fuel petcock (fuel filter is located between there and the motor if that matters) to the off position while the mower is running, the motor smooths out and runs fine till it runs out of gas. The second I turn the petcock back to on, the motor goes to cutting up and sputtering, missing, etc... Any suggestions on what the problem could be?