Mikuni Pump Around Carb Diagram
Since the 1990's, karters have utilized a fuel system called a pump around style. For years, this was the go to way of plumbing the carburetor, which was designed for a gravity flow system, to keep it functioning on a shifter kart appliation.
The basic ideas is to remove the float, inlet valve, and float needle valve, replacing it with a fixed scavenger tube. In theory, this would simulate the float height and fuel level in the float bowl.
The system uses two pumps, commonly mounted to a pump plate. One pump (A) was the supply pump, plumbed from the fuel tank, to a fuel filter, to the pump, and finally to the OE inlet on the carburetor. The second pump (B) was plumbed to the scavenger tube which was an aftermarket install on the side of the carburetor, and returned back to the fuel tank on the front of the chassis.
Over the years, karters have tried variations on the pump around, single pump systems, and / or the gravity feed systems.