This is a Holley 1940 carburetor.
The part in question is the Needle and Seat assembly.
When the floats drop, the tab sort of drops too, the "pin" moves outward and allows fuel to enter the bowl. When the floats rise (due to the bowl getting full of fuel) this tab pushes the pin in, stopping fuel from coming in.
There are several YouTube videos for this carburetor, I found a picture for you below.
Keep us posted with progress!
The Medic
Image (Click to make bigger)
Friday, June 8th, 2018 AT 7:35 PM