It happened long ago with real gas. 69 440 HP DD Ya it had a few miles on the motor. It did back fire and started running rich. I took the carb apart and found the float sitting on the bottom of the bowel. When I removed the float and shook it there was liquid in it but did not leak. There was a small sooty black mark around a bright spot in the solder on the float. This was just under the opening on the driver side where the accelerator pump is located. Some solders melt at fairly low temps. Apparently the solder melted long enough to allow some fuel inside and as it cooled resealed the float. Gas in an open container doesn't explode it burns. So I guess with an open source of fuel a little oxygen and a ignition source it can't happen. Aerodynamically Bumble Bees can't fly either