the big question is whether you had the petcock on or off?
Is your bike a California model by any chance? They have the closed fuel system, if the tank is overfilled Im not sure where it would overflow.
On my 49-state VS650 when I overfilled the tank on a cold day, when it got warm it came out thru the gas cap, and covered the top of the gas tank, and dripped down on the left side of the bike.
the other possibility is you got a stuck float. with the petcock left open most of the gas would come out the overflow tube, and spill on the top left center of the engine block (if the tube is attached). Whether that could find its way onto the exhaust pipe and look like it was coming from there, I cant say.
The exhaust on your bike has a heat shield fake outside everywhere, and its not air tight. I would think if you had fuel flooding into the exhaust from the cylinder being filled, the exhaust inner pipe would be sealed, and the only place it could leak out would be the opening (tip) at the end. The bike would have to completely fill the pipe for it to get that far, and when you started the bike it would shoot burning gas out like a flame thrower.. You did not mention that happening.
Like others have said, dont start the bike again till you get to the bottom of this. A little bit of gas in the oil will dilute it down from 20W40 to 2W5 - it will be too watery to build enough pressure for the bearings to float on a stream of oil, and it wont take long to eat your bearings.
The really safe thing to do is clean the pan you use to drain your oil till its spotless, then drain your oil out, and then measure it. With the oil still trapped in the filter you should only get about 2.7 quarts out (measure it)
if you drain out more than that, and esp if you drain out more than 3 quarts, then you got gas in your oil. You should also be able to tell just by smelling it.
If the oil is the right amount and does not smell like gas, you can put it back in the engine, or if its about time anyway replace the oil and filter.
If its got gas in the oil, take the filter out too, let the bike drain overnight with the plug out and the bike on the kickstand, and you will be ok to put in new oil and filter.
Also trace down the carb overflow tube and see if anything is coming out of it with the petcock on and the ignition key on so the fuel pump will run.
Again: chances are the tank overflowed and spilled out, and it just looked like it was in the exhaust. The fact that you rode it to work and it ran normally also makes it doubtful the carbs were overflowing.
But repairing the engine because the bearings are destroyed would be so expensive its worth a few hours of your time to make sure the carbs are not flooding the engine oil sump with fuel.
Last edited by KCW; 06-01-2019 at 05:50 AM.