Mower starts when cold but will not restart when hot. No problems for the first 300 to 400 hours on engine (this was a replacement 420) on a scag SWZ, we have switched stater and coil off the original engine that had a bad crank, still have same problem, starts when cold-wont restart hot & if left idling it will stall. We have fiddled with all the safteys on the mower and dosent seem to be that. We even added the square piece to the side ( some call it the ignitor)The new replacement engine did not have this piece, but either way-same results. Engine will start dead cold but will not restart until it has cooled for quite a while. A real nightmare out on the job. Appreciate any helpful advice. Mower repair shops in our area are NOT an option. They are expensive ($65.00 an hour) and our mechanic is generally more experienced.