GMC 4000 Series Service Manual page 336

If "Governor Calibration" results in a surging or
sluggish condition, correct as instructed under
"Correction For Surge" or "Correction For Slow
Opening" following:
Correction For Surge
Adjustment for surge must be made only to
point of removing surge. Over-adjustment will re­
sult in slow governor opening. Method for remov­
ing surge is as follows:
1. Break seal and remove adjusting cap. In­
sert hollow wrench into adjusting screw housing.
Insert 1/8" socket head setscrew wrench into ad­
justing screw.
2. Turn socket head setscrew wrench clock­
w ise, one-half turn, then holding it firmly, turn
hollow wrench cl.ck w ise until desired no-load
speed is reached. Repeat in one-half turn incre­
ments until surge is eliminated.
NOTE: Do not set governor to permit engine
rpm to exceed lim its listed in "Specifications."
3. Road test vehicle for elimination of surge.
When satisfactory adjustment has been made, re­
seal governor.
Correction For Slow Opening
Correction is made in same manner as cor­
rection for surge; except turn socket head set­
screw counterclockwise and hollow wrench coun­
terclockwise. Make adjustment for slow governor
opening very carefully as over-adjustment will
cause surge.
Dirty Governor
When sluggish action gradually causes vehicle
speed variations which grow exceedingly worse, a
dirty governor is indicated. Only remedy is to re­
move governor so that faulty unit can be disassem ­
bled, cleaned, reassembled, and calibrated as
previously directed. If governor is adjusted when
dirt is cause of unsatisfactory operations, engine
may be overspeeded under some conditions, caus­
ing serious damage.
Cleaning Air Filter
Occasional cleaning of governor air filter is
necessary. This element is assembled in governor
body beneath a perforated cover. Clean as follows:
1. Pry out metal cover carefully with a sharp
punch. Do not damage projections in governor
body. Lift out filter felt and inner cover. Wash felt
in cleaning solvent (gasoline, dry-cleaning solu­
tion); then allow to dry.
2. Blow out stabilizer cylinder and piston by
directing air in sudden bursts through atmospheric
hole in governor air cleaner chamber.
3. Install inner cover; then install felt in gov­
ernor body. Install outer cover. It may be neces-
G M C S E R V I C E M A N U A L
sary to bend cover to install; if so, flatten by tap­
ping with hammer (fig. 14).
GOVERNOR REMOVAL
associated parts, note position of governor spac­
ers, and also note number of gaskets used. This
will assure installation of parts in their original
position later.
controls from carburetor and remove carburetor
and governor.
GOVERNOR INSTALLATION
is not installed upside down. Governor is marked
with an arrow indicating carburetor side.
vacuum passage in some carburetors and under no
circum stances should this screw be left out when
installing governor.
buretor and governor is slotted to allow vacuum to
by-pass through governor for operation of power
jet piston. Make sure that this gasket is in good
condition and installed so that vacuum openings
are not obstructed.
ernor is operating correctly. When this is deter­
mined seal governor as directed.
of shaded items in figure 15. The hydraulic type
governor is used as standard equipment on 351-M
engines.
ated into the engine oil pump in engine crankcase.
The spinner valve is coupled to the engine oil pump
drive shaft and turns at same speed as the oil
pump (V 2 engine crankshaft speed). At one end of
the valve is a weight and at other end is a spring.
The spring holds the valve assembly in closed
position until such time as centrifugal force acting
on valve weight begins to move the valve toward
the open position. Governor valve calibration is
present to provide governor action at proper speed.
Engine speed control is achieved by permitting
pressure from oil pump to be applied at diaphragm
(5) in slave unit (fig. 16).
open position, the tension spring (3) in slave unit
causes the throttle plates (10) to move to wide-
open position. Diaphragm spring (4) holds dia­
phragm^) in its outer position and telescopic link
(7) is shortened as lever (8) on throttle shaft (9)
FUEL SYSTEM— GASOLINE ENGINES
NOTE: Felt is to be installed dry; do not oil.
IMPORTANT: Before removing governor and
Remove air cleaner; then disconnect lines and
1. Care should be taken to see that governor
2. A by-pass screw is installed in power jet
3. On some vehicles the gasket between car­
4. Road test vehicle to make sure that gov­
HYDRAULIC TYPE GOVERNOR
The hydraulic type governor system consists
NOTE: Key numbers in text refer to figure 16.
The hydraulic control mechanism is incorpor­
When accelerator pedal is depressed to wide-
Sec. 6M
Page 325