Motorcycle Questions? Ask a Mechanic.
This is most often a problem with the automatic fuel petcock valve leaking fuel into the vacuum hose and then into the air box one way or another.
There is also a vent hose on the fuel filler which can fill with fuel when the tank is full or tank pressure is high like on a hot day.
I would route the vent hose away from the air box and see if the petcock valve has fuel in the vacuum hose. Try replacing the petcock
or get some kind of shut off valve to stop the fuel manually.
Check your oil for fuel and change it if necessary.
A steady leak could be a dirty or worn carb float needle valve
inside the carb. This could flood the engine with fuel.