GMC 4000 Series Service Manual page 335

Sec. 6M
Page 324
FUEL SYSTEM— GASOLINE ENGINES
Figure 12— Operating Spring Coils
CHECKING GOVERNOR OPERATION
With engine idling, open throttle quickly and
observe engine response. If engine is slow or slug­
gish, basic setting of operating spring may be
wrong or governor may be dirty. If engine reaches
top speed quickly, then surges erratically between
high and low speed, improper spring setting or
faulty stabilizer action may be the cause. In either
case, cleaning and adjusting of governor is neces­
sary.
When erratic governor action occurs, clean
air filter felt. Replace filter felt if necessary.
GOVERNOR ADJUSTMENTS
NOTE: Make sure engine is at normal operat­
ing temperature and tuned properly. Illustrations
are of the single throat-type governor, but they are
also applicable to the dual throat-type governors.
Governor Calibration
To obtain proper calibration, governor should
be adjusted in following manner:
1. Remove governor as directed under "Gov­
ernor Removal."
2. Remove cover from governor and rotate
throttle valve to separate coils of spring (fig. 11);
then count active coils of operating spring in man­
ner shown in figure 12. Active coils begin at cam
ribbon anchor and end at beginning of adjusting
screw pilot thread (fig. 11).
3. Remove governor seal and seal cap. Using
1 /8 " socket head setscrew wrench turn adjusting
screw until number of coils remaining in spring
are as shown in "Specifications" at end of this se c ­
tion for this particular governor.
4. Install governor cover with slotted screw
and drive screw. Use an oversize drive screw if
necessary to hold cover securely. Refer to "Gov­
ernor Installation," and install governor.
5. After engine has reached normal operating
temperature and tuned perfectly, install a tachom­
G M C S E R V I C E M A N U A L
Figure 13— Calibrating Governor
eter to determine actual engine rpm.
27941) to adjusting screw bushing, and socket head
setscrew wrench in adjusting screw (fig. 13). Ac­
celerate engine and run at wide-open throttle.
coils, hold socket head setscrew wrench in one
hand, and rotate hollow wrench to change tension
on spring assembly with the other hand.
crease governor speed. Turning it left will de­
crease this speed. Turn hollow wrench to produce
a speed 25 to 50 rpm above speed shown in "Speci­
fications," with throttle still wide open.
tap lightly on hollow wrench until specified speed
is obtained. This operation is to seat adjusting
screw bushing in governor body. Remove hollow
wrench and install adjusting screw cap.
through hole in cover screw, adjusting screw cap,
and female half of seal. Twist ends of wire to­
gether securely inside female half and insert male
half. Also seal carburetor forward mounting bolt
in same manner.
Special Adjustment
ice or has been in service for a short period of
time, operator may for purposes of policy, or as a
result of experience, desire a setting on governor
other than that originally established. This may be
accomplished exclusively with use of regular gov­
ernor adjusting screw cap (8, fig. 8) as follows:
Check governor setting against tachometer and
turn adjusting screw cap clockwise to decrease
speed or counterclockwise to increase speed.
set faster than settings shown in "Specifications."
Figure J 4 — Spreading Filter Cover
6. Assem ble hollow wrench (King-Seeley No.
7. Taking care not to change number of active
8. Turning hollow wrench to right will in­
9. Remove socket head setscrew wrench and
10. Seal governor by passing sealing wire
In certain cases when vehicle goes into serv­
1. Remove seal from adjusting screw cap.
2. Under no circumstances should governor be