It's been a long time but...
1: Pressurized fuel from the selector switch
2: Crank case 'signal' that drives the fuel pump diaphragm (very thin piece of plastic in the stack)
3: Pressure occilations for the gas tank that work with the check valve to make pressure in the tank (goes to the fuel tank, one of the two 'non pickup' connections)
4: Fuel return, excess fuel is returned to the fuel tank (goes to the fuel tank, one of the two 'non pickup' connections)
Bob