Chevrolet 10 Series 1968, Service Manual

Page: 402 / 713

ENGINE FUEL 6M-9
the throttle body with the four screws provided. To
be certain that the throttle lever and throttle shaft
are in proper relation hold the throttle valve closed
while attaching the throttle lever assembly. Position
the throttle lever during assembly so that it fits
easily onto the throttle body. If this procedure is
followed the assembly will operate freely and
correctly.
2. Place the governor housing to throttle body gasket in
place, noting that the narrower edge goes toward the
top of the carburetor. Then put the housing in place
over the gasket.
3. Slide the leather seal and retainer over the throttle
shaft, position the screw holes in correct relation
and install the housing to throttle body screws
loosely.
4. Check the throttle shaft for free rotation in the seal,
then tighten the housing screws. The throttle valves
must be held in a closed position while tightening the
screws. Recheck for free rotation and repeat as­
sembly procedure if necessary.
5. Install the diaphragm in the governor housing with
the end of the diaphragm rod pointing inward. With
the diaphragm in this position the hole for the vac­
uum passage in the diaphragm should line up with the
vacuum passage in the housing. Assemble the gov­
ernor lever and pin assembly to the diaphragm rod
and position the lever on the throttle shaft. Install
the nut and lockwasher, holding one of the throttle
valves between thumb and forefinger while tightening,
to avoid damage to the throttle valves.
6. Position the diaphragm carefully over the screw
holes in the housing. Position the cover so that
cover restriction pilots through the gasket and into
the vacuum passage in the body. Install the eight
screws finger tight. Open the throttle valves wide to
provide maximum travel of the diaphragm and tighten
the eight cover screws to 25 to 28 inch pounds of
torque while holding the diaphragm in this position.
Install lockwire on screws (shown in Figure 3G).
Install the governor spring over the lever pin and the
stationary post in the housing.
7. Check again for free operation of the throttle shafts,
then install the governor, cover and four attaching
screws, and install lockwire (shown in Figure 3G).
8. Attach the pump rod and fast idle cam to the throttle
lever assembly.
9. Install vacuum tube to diaphragm cover and distribu­
tor and install lockwire in attaching nuts (fig. 3G).
TROUBLE
(2G VACUUM SPINNER TYPE)
1. Loss of speed control:
Check for vacuum leaks and operation of bleed valve
in distributor. Also for proper seal of diaphragm
cover and condition of diaphragm itself. Vacuum in
the governor housing can be checked by removing the
connection to the distributor and attaching a vacuum
line. If there is no vacuum reading check the dia­
phragm for holes and be sure the vacuum passage is
clear.
2. Erratic operation under load:
Check for binding in throttle shaft and throttle lever.
NOTE:
Vacuum and free operation are two
keys to correct operation of the Rochester gov­
ernor. If all parts are free to move as intended
and there are no vacuum leaks, the unit will
operate correctly.
Governing systems generally malfunction in one of two
ways:
1. They do not govern at all. This could result from:
a. A vacuum leak in the units or tubing.
b. "Spinner" unit stuck due to dirt, oil, or some
other material depositing in the mechanism.
c. Orifices in the carburetor clogging so no vacuum
could be developed in the governing system.
2. The system "over governs": governs when it should
not, causes loss of power, etc. This could result if
the vacuum passages were to become clogged with
dirt, oil, or other foreign materials. Areas most
likely to "clog" are the orifices in the actuator, and
the area where air bleeds through the distributor
"spinner" valve.
Either type of malfunctioning could be caused by:
improper spinner setting; spring post out of position in
SHOOTING
the carburetor actuator; bent or stretched spring in
actuator.
SUGGESTED PROCEDURE FOR FINDING
CAUSES OF IMPROPER GOVERNING
1. Localize the trouble on the vehicle. With the vacuum
tube disconnected at the distributor, run the engine at
about 3,000 rpm and place a finger over the end of
the tube. If there is no noticeable change in engine
operation, the trouble is probably in the actuator or
tubing. If the engine speed is noticeably affected by
this, the distributor "spinner" can be suspected.
2. If distributor trouble is indicated perform the follow­
ing operation (refer "Ignition System, Servicing units
off the Vehicle" in Section 6Y for detailed operation).
a. Remove distributor from engine, remove spinner
valve and clean and visually inspect the parts and
passages for possible faults.
b. Check the seals. Do this by connecting the lower
vacuum connector to a vacuum pump, and "plug­
ging" the valve hole in the shaft either with the
fingers or other suitable means. Slight "seepage"
around the seals is not abnormal; however, a vac­
uum gauge reading within 2" hg. of the maximum
that can be obtained with the vacuum hose
"squeezed" should be possible if the seals are in
satisfactory condition. If the seals leak exces­
sively they should be replaced.
c. When the spinner parts are reassembled, they
should be wiped with a rag saturated with light oil
to provide slight, but not excessive lubrication.
3. If actuator or tubing trouble is indicated:
a. Remove the vacuum tube at the actuator, run the
engine at about 3000 rpm and place a finger over
the end of the actuator. If there is no change in
CHEVROLET TRUCK SERVICE MANUAL