Mower has 92.1 hours on it. I pulled up to the truck and shut it off to air up tires. Immediately I decided to start it back up and put it on the trailer and just air up at the next stop. When I went to start mower engine turned over about six times but it didn't start. Out of the corner of my eye I seen fire. I don't mean it backfired. I been in business for years I know the difference. There was a ball of slow burning fire out of both exhaust openings the size of a basketball. I jumped of the mower and grabbed the fire extinguisher in truck to turn around and see that it was out. It burned long enough to leave burn marks all over sides of mower. It didn't get hot enough to bubble paint. I waited 30 minutes and started it. It ran fine all day with no problems. Piston Slapper? Restorob? Any thoughts. Was it operator error in some way. I've never had anything like this happen ever.