My Z44 doesn't want to start. Engine is turning over fine. I just greased it and pulled the blades, sharpened them and reinstalled yesterday. Started fine this morning and drove it out of shop, it stalled, restarted, died again and now won't run. I thought of the stop switch in the seat but see no sign of a broken wire. Checked spark, looked weak so installed new plugs to no avail. Could something have happened to the stop switch involving the PTO?