FUEL TANK.

TM 10-3930-623-12

When the piston reaches the top of its travel on the

e. Remove 4 nuts (3) and washers (4 & 5) which

compression stroke, both valves remain closed, and the

secure the fuel tank to the side of the truck body.

compressed fuel charge is ignited by the spark plug. At

f. Move the bottom of the fuel tank toward the

this time, the power stroke begins.

center of the truck and clear the support plate. Lower

fuel tank until fuel filler tube clears opening in truck body

4-9. POWER STROKE. Both valves remain closed

and lift tank from truck.

through this stroke. A spark, timed and delivered to the

spark plug by the distributor, has ignited the compressed

2. Installation.

Reverse removal procedure and

fuel charge. Burning the fuel charge raises its pressure

install the fuel tank.

to about four times the pressure in the cylinder before

ignition occurred, exerting a strong downward push on

4-14. CARBURETOR. The updraft carburetor used on

the piston, thereby turning the crankshaft to power the

this vehicle is a device for simultaneously vaporizing

vehicle. Some of this power, of course, also carries the

liquid gasoline and mixing it with air being drawn into the

other pistons through their nonpower producing strokes.

engine in a ratio suitable for use as fuel. The carburetor

At the bottom of piston travel on the power stroke, the

includes a throttle valve, controlled by the accelerator

exhaust valve is opened to permit escape of the burned

pedal, which governs the amount of fuel (air-fuel

fuel during the next exhaust stroke.

mixture) admitted to the engine to control speed and

power of the engine. The carburetor is mounted on a

4-10. EXHAUST STROKE. The burned fuel charge is

flanged opening of the engine's intake manifold. As

now worthless and must be disposed of to make room

each intake stroke takes place, air is drawn through the

for a fresh charge on the next (intake) stroke. The piston

carburetor bore and intake manifold to the intake valve

now is pushed up by the connecting rod and crankshaft,

of the cylinder on the intake stroke. As the incoming air

pushing out the burned gas through the valve to the

passes through the carburetor bore, it picks up a

exhaust manifold. When the piston has reached the top

quantity of gasoline (proportional to the amount of

of its exhaust stroke, the engine has completed one

passing air) to form the fuel mixture burned by the

cycle.

engine. The carburetor throttle valve is positioned in the

path of the air-fuel mixture, opening and closing to admit

4-11. Since a! this stage one cylinder, piston and intake

more or less fuel to the engine, as required.

and exhaust valve have completed a full cycle, each of

the others has also completed a full cycle. The cycle

4-15. ENGINE SPEED GOVERNOR. The governor is

described is repeated as long as the engine is running,

required to limit engine speed to 2500 rpm, without

once for each two revolutions of the crankshaft.

limiting power output below this speed. The throttle

valve is opened through a spring operated by the

carburetor linkage. The governor responds to engine

4-12. FUEL SYSTEM.

speed only, to override the tension of this spring and

4-13. The fuel system consists of the fuel tank, the

limit throttle opening regardless of gas pedal position.

mechanical fuel pump (actuated by an eccentric on the

However, should load increase while the engine is

camshaft) and the carburetor, with their connecting fuel

operating at governed speed, the governor will react to

lines. The fuel pump transfers gasoline as needed from

the resulting drop in speed immediately to permit the

the fuel pump to the carburetor.

throttle valve to open wider, increasing available power.

This process would be reversed if load decreased while

4-13.1.

FUEL TANK.

operating at governed speed. In actual operation there

will be a difference of about 200 rpm between unloaded

1. Removal. Refer to figure 4-1.1 and remove the

and fully loaded governed speed, to provide a working

fuel tank as follows:

range within limits of the governor's sensitivity.

a. Disconnect the fuel line (1) from the fuel

shutoff valve (7).

Adjustment

b. Drain fuel tank; remove drain plug (2) located

a. Connect a tachometer to the engine to read

on fuel tank bottom and drain fuel into a suitable

engine rpm.

container.

b. Start and warm up engine to operating

c. Loosen jam nut (10) and unscrew fuel filler

temperature.

cap assembly (8) from fuel tank (6). Remove cap

c. Loosen locknut on speed adjust screw (fig.

assembly by lifting until screen clears top of fuel filler

6-8) and adjust screw down to increase governed

tube.

speed, and up to decrease speed. Adjust governor to

d. Disconnect wire from the sending unit (13)

limit engine speed to 2500 rpm.

terminal.

4-2