Yuh-huh! It happened to me. Really. Today.
Driving down to Napakiak, doing about 45 mph, on the river, about 2-inches of hard snow so minimal resistance to forward movement. Just groovin' bey-beh...and what are all those flames shooting out of the hood!!!
Slam on the brake as I reached for the ignition to turn off (thought it might be electrical), jump off, throw the backpack clear (thought it might be a broken fuel line), open the hood and see the flames are all around the front of the muffler. Begin throwing snow on them as quickly as I can humanly scoop and see them disappear pretty quickly. Also put the flame out on the hood (it was on fire too).
Looks like the Arctic Cat briefcase-sized muffler got too hot and radiated heat melted, then caught the plastic bellypan on fire. It was an interesting 20 seconds of my life I tell you what! While I was unlatching the hood to get it open, I actually thought to myself, "well at least I have full coverage insurance". Kind of odd the things that go through ones mind during a crisis.
So now to the shop in the morning to find out what to do about this. I am going to cut away all the plastic from that area, and rivet in thin aluminum in which I have drilled lots of 3/8" holes to allow airflow around the muffler. I'll do the same along the bottom of the pan and install a sheet to protect the side of the hood area from radiated heat.
While driving back from Napakiak, I had both feet on the bulkhead to hold the hood up as it had buckled from the heat and wanted to lay on the stinger coming off the expansion chamber. I was able to watch the stinger and front half of the muffler start to glow dull red, through orange and into yellow within the space of 10 seconds or so when I stayed between 20-25 mph. At first I didn't even believe what I was seeing until I stopped to shut down the motor and let everything cool for a few minutes. Then I did the same thing again. After this I experimented finding I could keep the pipe cool as long as I was about 30 mph. Anything above 35mph and the pipe would not become incandescent. Pretty crazy. For some reason as yet unknown, at low speeds/engine rpm's/carb opening, quite a bit of gas is getting into the motor and burning very late in the pipe/muffler.
More to come.