The mower quit in the middle of mowing the yard. I checked and then replaced the air cleaner ans the gas line filter. It ran for about 30 minutes then would not run with the PTO engaged. Now it will start, rev for a few seconds then die. I think its a bad safety switch but am unsure as to how to trouble shoot this. Any suggestions? A service center is the last resort this time of year - they all have 2 to 3 week backlogs right now.