fuel. Secondary filters (fig. 1-23) are fabric filters thathave greater filtering qualities than primary filters. Theyarc used principally as the primary filter to protect thefuel injection pump.GASOLINE FUEL SYSTEMThe three basic parts of a gasoline fuel system arethe fuel tank, fuel pump, and carburetor. Fuel is suppliedfrom the fuel tank to the carburetor by either a gravity-feed system or a force-feed system. The gravity-feedsystem has the fuel tank placed above the carburetor(fig. 1-24). Afloat attached to a valve allows fuel to enterthe carburetor at the same rate at which the engine isconsuming it. This system maintains a uniform level inthe carburetor regardless of the amount of fuel in thetank. The force-feed system (fig. 1-24) is where the fueltank is located below the carburetor and a fuel pump isrequired.Fuel PumpThe fuel pump draws the gasoline through a fuel linefrom the tank and forces it to the float chamber of thecarburetor where it is stopped. Several types of fuelpumps are used; however, the most common type is themechanical nonpositive fuel pump (fig. 1-25).CarburetorFigure 1-23.-Secondary fuel filter.The carburetor is basically an air tube that operatesby a differential in air pressure. It has an hourglass-shaped tube called a throat and the most constricted partFigure 1-24.-Fuel systems.1-18
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