The Stovebolt Site Forums The Parking Lot Big Bolts COE carb fire

I'm working on my 1947 (1st series) COE and I went to start it yesterday. I know you're not supposed to pump the carb to start it, but I may have moved the throttle a little bit. When I tried to start it, it popped once and didn't start. On the second try it started, then sputtered and backfired. This ignited the excess gas in the carb elbow and she started burning. I don't have the air filter or intake runner on it. After a few attempts at blowing it out, I got the fire extinguisher and put it out.

My question is this, did I do something wrong? Would it have caught fire with the full air system in place? Did moving the throttle just slightly the cause?

I don't think it was running out like a stuck float or dirty shutoff. Today I removed the carb and cleaned it all up. I didn't see any problems with the float and valve. I even tested the float with the top of the carb off while sitting on the bench.

I don't want to fear the beast.

Gas accumulating in the intake is a design problem with updraft carbs. That's why every one I've ever seen has a small drain hole in the lowest part of the intake elbow so the gas can run out. (except for Marine models which are plugged so the gas can't drain into the bilge and blow up the whole darn boat)
Your's may be blocked.
I have never seen an updraft that had an accelerator pump either, for obvious reasons.
Next time you have one that catches fire, pull the choke out and/or stuff a shop rag in it.
I always keep a CO2 extinguisher close to the engine area of my shop, won't damage anything and no clean up problem. On the other wall I keep the dry chemical for electrical fires or big fluid spills.
It's a good idea to fix the problems so it doesn't fire back through the carb in the first place.

Engine timing is off causing the backfire.
Tom

Cold, lean engines backfire. You probably didn't use enough choke. I like to use full choke and crank an engine until it fires without touching the gas pedal, then release the choke about halfway to keep it from flooding and stalling. Using a little choke for a couple of minutes during warmup is usually needed, depending on the outside air temperature.
Jerry