Left the petcock open overnight

I have an '81 KZ550A, and could not get the original vacuum petcock to stop leaking, so I replaced it with a manual petcock.  Its been running fairly well, but the other day, I rode and then accidentally left the petcock in the open position overnight.  I drained the float bowls, and fired it up. Seemed to run fine, but after a few minutes it sputtered and conked out.  I changed the oil and plugs, did not see any metal shavings or signs of fuel in the oil.  I can get it to idle fine, but when I down shift it sputters and dies. Help! Thanks,

Did the carbs overflow? Was there gas in the cylinders, airbox, or oil? Could it just be coincidence that the problem started after leaving the petcock on overnight?
I many times have forgoten to turn my petcock off without it causing an issue. 99% of the time the float needles keep the carbs from overflowing.
 

Thanks. No carbs didn't overflow. I think now I realize its more of a fuel flow issue. When I added the fuel filter I had to extend the fuel line and it has to run "uphill" a bit from the petcock. I plan to shorten the fuel line and create a more direct "downhill" flow from the petcock to the carbs. We'll see....