[.041 Safety Wire]

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.

Idle cutoff is a function of the mixture control not the throttle. This typically happens on start up if you are overly energetic with the primer as it puts too much raw fuel into the exhaust manifolds.