In walbro repair manuals they refer to the "pop off arm" and "pop off pressure" etc

The "Pop Off Arm" referred to is part of the zero pressure demand regulator.

Another way to think of the pop off valve operation for those of us who do not have Walbro pressure testers . . . .

It lets no gasoline pass by the needle and seat unless there is a slight vacuum on the diaphragm coming from the throttle area of the engine.

This allows only gasoline that is needed for the engine to pass the needle and seat

I suppose if you put enough fuel pressure behind the needle, it could eventually release and pop off but this is not part of the normal "in operation" of the carburetor.