1959 GM Rochester 1-barrel carb question

I have a 1959 GMC with a 270 straight 6 and a 1 bbl Rochester carb. It appears to be leaking fuel from a small hole in the upper rear part of the carburetor. Picture is attached.
Why would this hole be here? Should it be connected to something?
Thanks-
Mark

 

Bowl vent.

Fuel is leaking here because:

(1) Bad float
(2) Bad fuel valve
(3) Improper fuel valve/float adjustment
(4) Too much fuel pressure
(5) Cracked casting (exceptionally rare)

Jon

 

Thanks Jon!