Can we please stop assuming that fuel delivered by the accelerator pump while cranking will pool in the air box.
I choose not to, I've read the POH's.
The POH for the 150 says:
FIRES.
Engine Fire During Start On The Ground.
Improper starting procedures such as pumping the throttle during a difficult cold weather start can cause a backfire which could ignite fuel that has accumulated in the intake duct. ....
For both the Continental and Lycoming powered 172's, and the 182, the POH says:
IMPORTANT
Pumping the throttle may cause raw fuel to accumulate in the intake duct, creating a fire hazard in the event of a backfire....
The Beechcraft Musketeer POH is more brief:
Do not pump throttle to start
When I started my 150, which I had preheated for the cold day, I gave it the normal two shots of prime, and started it. It was not idling smoothly, which is usually an indication that not all of the cylinders are running yet, but all four usually catch after a few seconds. As the POH says, as it stumbled, I added a few more primer shots to keep it idling. It stopped, so one more shot of prime, and start again. It ran, then stopped. I saw the smoke coming up through the windshield defogger, knew I had a carb fire (and my wife was phoning me to tell me she could see it). So I pulled the mixture, opened the throttle, and cranked until the battery was discharged. I hopped out, and could still see fire in through the oil door, so I hit it with the fire extinguisher. It was the oil breather insulation burning, not terribly serious. But, the airbox, and carburettor were fire damaged, and the cowling discoloured.
Prior to that, I had twice been a passenger for a carb fire, once in a C180 amphibian, which is a bit more difficult to exit and extinguish in a hurry. My 150 is the only plane I have set fire to of the 283 different aircraft I have flown since 1975, and when I did it, I had over 3000 hours in 34 years of owning it - I did what the POH said to do - and still got it wring that day.
It's my goal posting here to provide my experience and whatever wisdom I have to give, to those who wish it - advice as to have the best success at safe flying. I will not be advocating procedures which contradict what a POH says. That's just me....