This style of Carter BB carburetor uses vacuum to operate the accelerator pump.
Stroke is non adjustable. Pump intake passage ball check seat size .115 to .120, 2.92-3.05 mm diameter.
Pump discharge jet size .0315.
This style of Carter BB Carburetor uses a rod that connects the top of the accelerator pump with a lever at the bottom attached to the throttle shaft. As the throttle is opened the accelerator pump is forced down into the pump well, squirting gas out of the main discharge.
Purchase pumps and related parts here
Example of a typical pump
B&B Pump Spring