Governors - GMC 4000 Series Service Manual

the engine running. The pressure should be within
the lim its given in "Specifications" for the par­
ticular engine. The pressure should remain con­
stant and return to zero when the engine is stopped.
CAPACITY TEST
To make the capacity test, connect a hose to
the disconnected fuel line at the carburetor inlet.
Place the hose in a pint measure held at carbur­
etor level. Run the engine at 1200 rpm's and note
the time it takes to fill the pint measure. Refer to
"Specifications" for time required for type engine
used.
FUEL PUMP REPLACEMENT
REMOVAL
NOTE: On trucks equipped with a shut-off
valve in fuel line, close valve before removing fuel
pump. Remove any accessories and piping which
would interfere with fuel pump removal.
1. Disconnect fuel lines at fuel pump.
NOTE: If tank line continues to siphon, remove
filler cap from fuel tank, then apply air pressure
into line to force fuel back into tank. Make sure
filler cap is reinstalled.
2. Remove pump mounting bolts, then move
pump away from engine and remove gasket.
INSTALLATION
Before installing fuel pump, be sure mounting
pad on engine is clean and that any gasket cement
or portions of old gaskets have been removed.
VELOCITY TYPE GOVERNOR
Velocity type governors are of two types and
designated as single-throat type and dual-throat
type (fig. 8). Single-throat type governor, having a
single throttle valve is used on In-line engines,
and the dual-throat type governor having two throt­
tle valves is used on V-6 engines.
Governor is mounted between carburetor and
intake manifold and operates on combination of
vacuum and the velocity pressure of in-going gases.
Speed adjustment is by means of sealed adjusting
screw.
Governor is adjusted for correct maximum
engine speed and sealed at the factory.
Refer to "Governor Specifications" located at
rear of this section before servicing governor.
G M C S E R V I C E M A N U A L
so eccentric on camshaft applies least tension on
pump arm.
pad on engine, then set pump in place and install
mounting bolts.
sure pump lever is positioned as shown in figure 7.
On vehicles equipped with the V-6 engine, pump
arm must be on bottom of camshaft eccentric
otherwise pump arm will be broken when engine is
started.
shut-off valve (if used).
to gain access for removing fuel pump.
evidence of leakage. Check pump for static p res­
sure as explained previously.

GOVERNORS

GOVERNOR OPERATION
control its operation. These are shown graphically
in figure 9 and are explained as follows:
Closing Force (Fig. 9)
against approximately 75% of the area of governor
throttle valve tends to push plate into closed posi­
tion. This action occurs by having the throttle shaft
off-center as shown in figure 9.
Opening Force (Fig. 9)
speed is reached, it is necessary to have an ever-
increasing "opening force" opposing the "closing
force." This is accomplished, as shown in figure
9, by the anchored coil spring, connecting ribbon
and cam attached to throttle shaft. The ever-in­
creasing spring tension plus the progressively
FUEL SYSTEM— GASOLINE ENGINES
NOTE: To facilitate installation, crank engine
1. Place new fuel pump gasket at mounting
IMPORTANT: When installing fuel pump, be
2. Connect fuel lines to pump, then open fuel
3. Install all accesso ries or piping removed
4. Start engine and check line connections for
Three force system s, set up within governor,
A strong velocity pressure of air-fuel mixture
To maintain constant control after top engine
Sec. 6M
Page 321