OK, so if you have over primed, with the fuel in the cylinders, where does the fire start?
Depends where the fuel prime is directed within the engine......And depends on the type of engine. I've seen induction fires after overpriming, and also seen a pool of fuel catch fire that had dripped out after the guy was pumping the throttle.
However, one aircraft I fly (0-540 x 2) will not start in this icy weather unless you pump the throttle as you crank the engine over.
I've also seen a PA28 (0-360, not an injected engine) that would only start when warm with the mixture control in 'ICO'
As with most things aviation, know your aeroplane...
And if in doubt, start from lean and work up to rich rather than the other way.