The fuel cutoff is not working. Fuel is dripping from the bottom of the carb and from the drain line.
Okay, you have a float level issue, or a dirty needle/seat valve for fuel shutoff.
Turn the petcock off at the tank, and remove the carburetor.
Unscrew the screws out of the float bowl, and remove it and clean it out.
Try not to wreck the gasket, unless you have a spare gasket.
Slip the axle out of the float assembly, and dump the movable piece out of the needle/seat valve, and check to see that the pointy end was "up", and that it looks clean and not worn.
Spray some carb cleaning up in there, and all around in the float bowl.
Put the float back on, and check to see it looks pretty level when you hold it upside down. If you have the workshop manual, check the float height according to the instructions.
Put it back together and install it on the bike, and see if that fixes it.
It basically works just like the float shutoff in the tank of your toilet.
Same principle.