fuel leak

[97dime]

my bike started leaking fuel today.  i started to work today and about 3 miles down the road it stated spitting and sputtering like i was out of fuel.  i switched it to reserve and it was fine.  couple miles later i stopped at a stop sign and it stalled and wouldn't restart.  then i stated smelling fuel.  i noticed it was leaking from the vent tube between the carbs and the air box vent.  no matter which position i put the frame petcock in it leaked.  in the on and reserve positions it dripped and in the prime position it was a constant run.  could it be a stuck float or something.  i'm not to familliar with carbs.  most of my experience is with fuel injected cars.  any help would be appriciated.