GMC 4000 Series Service Manual page 333

Sec. 6M
Page 322
FUEL SYSTEM— GASOLINE ENGINES
1 Governor Body
2 Valve Shaft
3 Throttle Valve
4 Throttle Valve Arm
5 Stabilizer Piston Rod
6 S t a b iliz e r P is to n
7 Stabilizer Piston Plug
8 Adjusting Screw Cap
increasing radius of the cam builds up an "open­
ing force" to oppose and balance the "closing force"
on the throttle valve. Actually, under operating
conditions, throttle valve does not close but a s­
sumes a position between point "A" and "B" to
give proper amount of air-fuel mixture to limit
speed of engine to governor setting.
Stabilizing Force (Fig. 9)
A sudden manipulation of the throttle will
often result in the opening of governor throttle
valve and permit engine to exceed governed speed.
G M C S E R V I C E M A N U A L
3 SINGLE TH RO AT TYPE
4 5
W ITH DISTRIBUTOR
V A C U U M A D V A N C E
9 Adjusting Screw
10 Adjusting Screw
Bushing
11 Governor Cover
12 Operating Spring
13 C a m R ibb on
14 Cam Ribbon Clip
15 Roller Bearing
Figure 8 — Velocity Type Governor
Figure 9 — M ajo r Controlling Forces of G overnor Operation
D U A L TH RO AT TYPE
11 12
16 Vacuum By-Pass Passage
17 Roller Bearing
18 Sh aft P lug
19 Transfer Valve Spring
20 Transfer Valve
To counteract this condition, a stabilizing force is
set up as shown in figure 9.
Stabilizing piston is open on inside to vacuum
above governor throttle valve, and is open on out­
side to atmospheric pressure through a felt air
filter. Piston linked to throttle valve acts to close
valve when a vacuum draws piston toward governor
throat, thus offsetting any tendency of the increased
vacuum, due to carburetor throttle valve manip­
ulation, to open the governor valve. This action
controls smoothness of governor action.
13
r-i
8 7 5