My mower is a 2003, 60" Lazer with the 26hp Kolher EFI with 1100 hours. All but two of my lawns are small (under 10k sq ft.). Well, im cutting one of those small lots, finish up, mower runs fine and everything, load it in the trailer, still running good, go to the next lawn, try to pull it out of the trailer and it had no power, a hissing sound, running really rich, spark plugs really black. I put new plugs in, and same thing. Any idea what could cause this? O2 Sensor? Valve?