Ok....Here come some carburetor questions...

As I've mentioned, I took both of these carburetors off of this car. I haven't even started anything with them, but was just inspecting them.
Now..Does anyone know what the throttle (?) plates on the VERY bottom of the carburetor is supposed to do? I am trying to understand how it works...
When I turn the carburetor upside down, there are 2 of those flaps on the very bottom. One opens easily when the linkage bar is pulled back. The other flap has a bar that appears to go to the vacuum "circle" (that says Zenith on it). Is it SUPPOSED to open?? Ever?? Common sense tells me it should, since IT IS a flap...BUT on both of my carburetors, this flap doesn't open. If it helps, the flap that doesn't open, is the really dirty one...

Does anyone know what the hell I'm talking about??

~Christy