Like the others said, the carb is leaking gas through the float, and either needs cleaning or adjustment.
In your earlier post, you were looking for a fuel shutoff. You will find that the Ford N tractor fuel sediment bowl and shutoff valve will thread right into either of the two holes in your aftermarket gas tank. Not original, but much easier to repair or cheap to replace.
If you go this route for the fuel shutoff, the center hole in the tank will not offer enough clearance for an N sediment bowl assembly over top of the valve cover for the engine, so use the threaded plug here and close it off. Put the N fuel bowl assembly in the other threaded hole on the side and you will find that you can reach this from the seat of your 600. Very handy.
Doug in east TN