[Davew]

Absolutely real! I used to be an Air Craft Mechanic that stuff happens all the time. Now should he let it burn out? Be sure to lean the mixture, place the throttle in idle cut off, Shut off fuel cock (it should be there) and cycle the starter a couple of blades. It will go out. Better yet, KNOW the manufactures recomendations for this condition and correct it their way The fuel is not burning all the way and its in the exahust stacks. It could be a number of things. Radials are famous for lighting up.

These aren't engine fires though. They are due to the very rich mixtures that are run, the fuel being pumped into the cylinders before engine start, and are a common part of the start up sequence. The fuel is still burning when the exhaust stroke starts and is pushed into the exhaust. On the aircraft with longer exhaust stacks such as the radials you generally just see a puff of smoke on start up. But its due to the same thing.

Engine Fires are caused generally by excess priming, which causes large amounts of fuel to pool in the carburetor intake. This fuel can then ignite if the engine backfires. The reason most Pilot Operating Handbooks recommend that you keep trying to start the engine after the fire is noticed is because this puts the fire out by pulling the flames back into the engine.