6 pack center carb question

on the back of the carb body there is a plate with 2 screws, inside it looks like some sort of spring with a small brass plunger. This carb was missing pieces and I'm not sure if anything else goes in there. I can't find a diagram anywhere that shows this plate or the parts behind it. It is a 4791 carb and if someone could tell me anything about this it would be much appreciated. Thanks

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