I have a xMark with a Kohler 26 EFI and it is running rough the majority of the time. I have read through the forums and understand if there is a problem that the ecu instruct the engine to run rich. But how do you find out whats wrong? Their is no engine code light on. The unit runs just seems to run rich. I don't know where to begin to look. Grounds exhaust? O2 sensor? I checked the plugs and they are black from being rich. I couldn't find any solutions mentioned in the forums to the 26 EFI rough running problems? Can anyone help or suggest where to begin? How about the Oldguy?