Fuel Pump - TM-10-3930-633-120065

TM 10-3930-633-12

4-49. Fuel Pump

performed with the fuel pump installed on the

engine and the engine at normal operating

The fuel pump is mounted on the lower left center

temperature at idle speed.

of the engine cylinder block. The pump is of the

NOTE

mechanical diaphragm type, and is operated by

Before the tests, make sure the replaceable fuel

the rocker arm `which rides on an eccentric of the

filter has been changed within the recommended

camshaft.

maintenance interval. When in doubt, install a

The fuel pump incorporates a replaceable filter

new filter. Refer to paragraph 4-47.

element which filters suspended particles out of

b. Pressure Test.

the fuel before it reaches the fuel pump. This filter

(1) Remove the air cleaner assembly.

element is replaced every 500 operating hours.

Disconnect the fuel inlet line or the fuel filter at

t h e carburetor. USE CARE TO PREVENT

4-50. Fuel Pump Tests

C O M B U S T I O N DUE TO FUEL SPILLAGE.

a. General. To determine that the fuel pump is

(2) Connect a pressure gage, a restrictor and

in satisfactory operating condition, tests for both

a flexible hose between the fuel filter and the

fuel pump pressure and fuel pump capacity

carburetor, as shown in figure 4-25.

(volume) should be performed. The tests are

Figure 4-25. Fuel Pump Test Set-up

(3) Position the flexible hose and the

specifications, and the fuel lines and filter are in

restrictor so the fuel can be discharged into a

satisfactory condition, the pump is defective and

suitable, graduated container.

should be replaced.

(4) Before taking a pressure reading, operate

(7) If the pump pressure is within

the engine at 500 RPM and vent the system into

specifications, perform the tests for fuel capacity

the container by opening the hose restrictor

(volume).

momentarily.

c. Capacity ( volume) Test. With the fuel pump

(5) Close the hose restrictor, allow the

pressure within specifications, test the capacity

pressure to stabilize, and note the reading, which

(volume) as follows:

must fall between 4.0 and 6.0 PSI.

(1) Operate the engine at 500 RPM.

(6) If the pump pressure is not within

(2) Open the hose restrictor and expel the

4-39