This engine is model #252707 and it's on a MTD Lawn Tractor. It runs well, but if we shut it down after running it for a while it won't start. I have a tool to check the spark and found there is no spark. After sitting the mower in the shade and letting it cool down a bit, the spark comes back, and it runs great. I've checked the battery connections and grounds and can't see anything that would cause this. Any suggestioins??? Thanks.