Let's look at the fuel system in more detail. Fuel is drawn in through the filter(1) by the fuel pump (2) then pumped through the muffler (3) into the pressure line (4). The pressure regulator (5) is adjusted so that pressure in the line between 2 and 5 is maintained at 28psi. Excess fuel passes through a pressure relief valve in the pressure regulator (5) and returns to the tank. The bypass line (6) lets fuel return directly to the tank if there should be a fault in the fuel lines.