Carburetor will not fill with fuel.

I have a 71 VW Super Beetle with stock engine. My problem is my carburetor
will not fill fuel bowl with gas. It is a new unit, I have replaced fuel pump and
fuel tank. I have checked fuel line from tank to pump with compressed air and
it is clear.  Oddly, this is the second new carb I have installed with the same
problem with both. I removed fuel line form carb and placed in a bottle to che
k fuel flow from pump and there is sufficient flow. I can pour gasoline into fuel
vent on carb to fill fuel bowl and car will run fine until fuel bowl is empty. It
seems that needle valve is not opening to allow fuel to flow into bowl, but it is
odd that two carbs would have the same problem. Any ideas? Thanks !