Holley 1920 Carb question 225 - 6

Can't clearly see the hole you're pointing at. It's not the calibration hole present on many pre-1970 carburetors of all make and barrel count; that'd be over on the other side of the carb if yours has it. Could be the accelerator pump chamber vent. It doesn't sound as if you've verified that this is where the fuel is actually leaking from. The leak point could be from the external bowl vent in the case of a stuck or sunk float or a faulty inlet needle/seat. It could be from the bowl cover gasket. It could be from that hole you're pointing at if there are internal faults in the carb. It could even be from a cracked carb casting.

The "curb idle vent" (external bowl vent) is atop the carburetor, right up front, capped by a little round rubber hat on the end of a pivot lever. When the throttle is closed (curb idle) the hat is lifted off its seat, thus venting the carb bowl.

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

The float in a 1920 cannot "fill" with gasoline or get a hole in it; it's a nitrophyll foam float, not a hollow brass one. But they can take on fuel and grow heavy, causing the same problems. Also the float counterspring must be present.

Have you been through the carb with a rebuild kit and a new float yet?