My tractor is having a weird issue. It was running fine and I went to put some food plots in at the farm. About an hour into running the tractor it starting running rough and back firing. It was also lugging down and when I would give it more throttle it would take a while to catch up and almost cut out. Well I limped along to get finished and when I went to shut the tractor off with the key it kept running and really started backfiring and carrying on. I had to choke it out to get it to shut off. The tractor only seems to do this if it has been running for 15 minutes or more. I know I have heard of 12 volt conversions back feeding through the ignition if you don't put a diode or light in the wiring. The tractor had ran fine up until this day. Is it possible the ignition switch is shorted out and still making partial contact in the off position?