Fuel Tank venting control valve

[l.groves]

I've checked posts about fuel odor but thought I would check the venting system. All the vacums are working but I cant get any vacumreading from the Control Valve where it connets to the T connection. I tried testing it at idle and under acceleration and no vacum. There is an adjustment screw and lock nut on top but it didn't make any difference. Does this mean it is bad or is there another way to test it? It's on a 85a 944. This valve siphons the gas fumes to the intake hose..