The Edelbrock carburetor is set up differently from the Autolite 4100. "A" is the vacuum port for the vacuum advance. This port offers part-time vacuum when the throttles are opened. "B" is a larger full-time vacuum port, which isn't used in this application. This port gets plugged. "C" is a smaller full-time vacuum port for vacuum accessories in some applications, "D" indicates the idle mixture screws, and "E" is the idle speed adjustment screw.