help needed with Edelbrock 1405 carb

My 350 smallblock is fitted with an Edelbrock Performer RPM kit that includes a 1405 carburettor (600 cfm).
Because the power is lacking, I checked the operation of this
carb, but I cannot figure out how it is supposed to operate.
What I see is this: (image at ) 4 barrels, and the front two are chocked with a manual choke. When opening the throttle, I see the front two barrels open up. But the back two remain covered by an additional valve? It looks like the two at the back have two valves on top of each other and only the bottom is opened when the throttle is opened very far. But the bulk of the passageway remains closed due to the extra valves.
Is this normal? What are those top valves for, covering the rear barrels?
Also: I noticed that the intake gets very hot, and remains warm to touch even 5 hrs after driving, when headers and block have completely cooled.
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