My mower is 12 years old and has run well. Last year I took it to two different small engine repair guys who cleaned the carb and checked the timing, etc. Neither one could determine the problem and suggested I take it to a Sears repair. The mower starts just fine but runs for anywhere from 2 minutes to five and then quits. In trying to start it, it backfires and will not start again until it sits for an hour or so. Perhaps it is too old and needs to retire like me.