Or is it, as is the case with our's, that the drain screw is letting by. Haven't solved it yet. All that seals it is the taper on the screw.
Cheers
Min

Remove the screw, reface it with very fine sandpaper. Or maybe there is a bit of crap under the seat.

The drain screw outlet is also the overflow on some bikes.

Sent from my Moto G (5) using Tapatalk

Testing:

Remove float bowel.

Turn on fuel

fuel should now be running out!

move float upwards .. this should stop the fuel flow. If it does not then you have a problem there.

Left float fall - fuel should start flowing again, move float upwards gently and make certain the fuel flow shuts off again.

-------------------------------------- It is a very simple test. Saves dismantling to look.

Check the brass overflow pipe at the base of the carb bowl is not pulling air [ fill it with some fluid and attach an air line]
Easy fix is a small amount of chemical metal around the base of the brass pipe taking care not to block the drain port of the bowl