is this happening while the bike is just sitting, or while ur driving?
if its when ur sitting, is ur fuel selector in the "ON" position? (pointing straight down) or in the prime or "PRI" position (pointing towards the back of the bike) If its in "PRI" it will allow fuel to flow freely into the carbs, with gravity helping it along, and can over flood the carbs (i had this problem when my bike was parked for 7 year, over filled the crank case with fuel/oil)
when its in the "ON" position, fuel cannot flow down the fuel lines until the engine is running do to the vacuum diaphragm turn on. basically, that lil black line that goes from ur carb vacuum port to the petcock, provides vacuum to actually turn on the fuel to the carbs