I just mounted up a set of CR29 carbs and while I was hooking up the fuel lines i noticed an open tapped hole in one of the carbs, which is blanked off on each of the other carbs.
Each Carb has an air screw to one side of the inlet

and 3 out of 4 have a corresponding blanked off section on the other side of the inlet

However 1 out of 4 has a tapped hole oppostie the air screw

This hole must have a purpose.
Can anyone help?