How fuel climbs its way to the intake. Engine flood disaster.

[marc]

I've had my GS500 sitting in the garage for a month.

Last weekend went to crank it, the starter motor turned and turned, but it won't catch.

Recharged the battery and tried again, with no luck.

I got the spark plugs out, and one was wet and the other was dry. 

Cleant both, reinstalled but still not starting.

OK, carb problems, I disassembled tank, air filter, and removed the carbs.

I found that the float in one of the carbs was not working.
Ouch, went for a couple of float valve rebuild kit ($40 each ), installed, adjusted float height using the procedure somebody in this list explained (attach a U shaped piece of plastic tube to the underneath drain screw), and the carb was no longer overflowing.
Tested several times. OK problem solved. 

The bike started fine, bus as soon as I stoped the engine, a full drop of fuel was shoot out of the engine through the engine overflow tube; yes that tube that is on the head cover. 
Couldn't believe it. I cranked the bike again, started fine, revved, stopped, and again a full drop of fuel was shoot out of that tube.

Opened head cover, valves fortunately were still there  and saw nothing strange.
Since I was there, I made a valve adjustment.

I looked at the oil dipstick and... what? It was about two inches upper that it should.

I put a drain plate and opened the oil screw under the engine.

I got 8 litres (about two galoons) of oil mixed with fuel, out of the engine! 

Of course I spilled some of this mixture all over the garage and this caused third world war at home.

I am thinking about next:
I left the bike with the petcock in PRI position. Float valve failed to stop fuel, it overflowed into the engine intake, went to the intake valve that was open for sure, and reached the piston rings and the crankcase.

But... how did fuel its way to the engine, climbing to the intake, instead of making its way to the air filter box? 

If my approach is wrong, then, what happened? 

...and yes, I've been lucky that it did not catch fire when I started it twice, and the fuel shoot reached the hot exhaust tube. 

[hmmmnz]

ooh lucky. could have been bad, real bad.
i think you are along the right lines with the overflow into the engine ect, a similar thing happened to me, but i caught it straight away, and didnt have the bike sitting for a month,
you might have had a blocked overflow, or simply just a bubble that stopped the fluid getting past and the only place left was the engine.
don't leave it in prime. unless you just drained you carbs and have to refill them,
im glad you didnt wreck your engine

[MarkusN]

But... how did fuel its way to the engine, climbing to the intake, instead of making its way to the air filter box? 

Look again. Because of the tilted cylinder bank the path from the carbs into the cylinder is actually down. I think it's only thanks to the air jets, which sit a bit lower, that in most cases the fule drains into the airbox.