fuel. Secondary filters (fig. 1-23) are fabric filters that
have greater filtering qualities than primary filters. They
arc used principally as the primary filter to protect the
fuel injection pump.
GASOLINE FUEL SYSTEM
The three basic parts of a gasoline fuel system are
the fuel tank, fuel pump, and carburetor. Fuel is supplied
from the fuel tank to the carburetor by either a gravity-
feed system or a force-feed system. The gravity-feed
system has the fuel tank placed above the carburetor
(fig. 1-24). Afloat attached to a valve allows fuel to enter
the carburetor at the same rate at which the engine is
consuming it. This system maintains a uniform level in
the carburetor regardless of the amount of fuel in the
tank. The force-feed system (fig. 1-24) is where the fuel
tank is located below the carburetor and a fuel pump is
The fuel pump draws the gasoline through a fuel line
from the tank and forces it to the float chamber of the
carburetor where it is stopped. Several types of fuel
pumps are used; however, the most common type is the
mechanical nonpositive fuel pump (fig. 1-25).
Figure 1-23.-Secondary fuel filter.
The carburetor is basically an air tube that operates
by a differential in air pressure. It has an hourglass-
shaped tube called a throat and the most constricted part
Figure 1-24.-Fuel systems.