If the float was stuck and the valve was hung open, gas would have
been coming out of the vents & such.  I would be surprised if
you DIDN'T smell gas.  

Many thanks for everyone who volunteered their opinions, but after
tearing the carb apart and finding NOTHING wrong, it has been quite a
witch hunt to find the REAL culprit. Here is what apparently happened:

The fuel pump developed a microscopic leak in its diaphragm, which built
up fuel behind it (the business side is on the bottom, so the gas
collected on the top of the diaphragm). There was a 1/4" hole in the
side of the pump to keep any leaking fuel out of the oil, so it leaked
out there and THAT is what we smelled for days preceding the
semi-disaster. When I removed the fuel pump, it dumped a teaspoon full
of gasoline onto my hand from that vent hole. Further, everything below
the vent hole was VERY clean.

When, we drove ~50 miles to town on a HOT day, loaded up our trailer
with a half a ton of stuff, and generally heated the engine block well
above the boiling point of the gasoline. With the PCV system in good
working order, the vaporized gasoline from the leak was sucked IN to the
crankcase, some went into the oil (that gained about 3 quarts in volume)
and the remainder went either through the PCV or the crankcase vent to
the air cleaner. I suspect that in the process the leak got a lot worse.

Curiously, once in this mode, we didn't smell any more gasoline -
because it was no longer leaking externally, but was all being sucked
into the engine!

In total, this hassle ended up including:
1. Tearing apart a perfectly good carburetor.
2. Changing the oil and filter.
3. Replacing the air cleaner.
4. Replacing the fuel pump.
5. Replacing the tank full of gasoline that was lost, this being the
biggest actual expense of them all!

I had just gotten back from a long trip in this vehicle. I shudder to
think how this story would have turned out if this had all happened on
the road. By the time some repair shop had replaced the carb, etc., I
could have been out a LOT of money.

Thanks again for everyone's comments.

Steve Richfie1d
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