My tractor is ten years old and in excellent shape it has been very well taken care of by me. It recently has had a problem wanting to start after it has been running for more than 30 min. Today it just decided to quit and now it will not start. I have removed the plug and checked the safety switch under the seat. Nothing I have done has helped. I recently put a new fuel filter on thiking this was the problem, but it still is not running the way it used to.:( Any suggestions?