Idle Air Vent

[MBP]

 Hello to all. My question is about the Idle Air vent on my 4MV. The piece with the rubber disc that connects to a lever via linkage that activates the Power Piston. The rubber disc doesn't appear to move when the accelerator linkage is moved or at idle. Should this disc be slightly open(raised up) at idle and if so how is this obtained, bending the linkage and if so by how much? As is now it is simple covering the vent and never moves to open. Thanks, hope this somewhat makes sense.

[Kenth]

I guess you are referring to the acc pump stem when you write Power Piston (the power piston holds the primary rods inside the float bowl).

Anyway, aim for 3/8" at measurement point #4.

[ourkid2000]

Curious, what does this vent do? Only reason why I ask is that it's usually blocked off on later or reman carbs.

[Kenth]

This:

[ourkid2000]

But doesn't the bowl vent (the tube sticking up) on the airhorn already expose the float bowl to the atmosphere?

[Kenth]

This:

[Cliff Ruggles]

You don't need the vent to be operational but it really doesn't hurt anything if it works or not.  When I build early carbs here I don't adjust the link from the pump arm over to the vent so it opens at idle speed but I leave all the components in place so it looks original.....