Exhaust Em Ission Control Systems; 2. Controlled Combustion System - Modified - GMC 4000 Series Service Manual

moved from closed to wide open position as shown
in figure 28. The pump travel is as indicated in
''Specifications." When necessary to adjust the
lever travel, bend the pump rod at the upper end.
305E, 305C, and 351C Engines
Operate accelerator pump to properly seat
checkball, then with throttle fully closed (idle
speed screw backed out), place a straight-edge
across the air horn and measure distance from
GENERAL INFO RM ATIO N
Since products of combustion in gasoline en­
gines contain contaminants which cause atmos­
pheric pollution, a means to reduce harmful em is­
sions must be employed. Devices used for this
purpose fall into one or more of the following cat-
agories:
1. Positive Crankcase
(P.C.V.).

2. Controlled Combustion System - Modified

(C.C.S.-M.).
3. Air Injector Reactor System (A.I.R.).
The first system serves to prevent air pollu­
tion by re-cycling fumes from the crankcase (used
on all engines). The other system s are used for
control of air pollution from exhaust system em is­
sions on vehicles sold in California.
G M C S E R V I C E M A N U A L
EXHAUST EMISSION
Ventilation System
FUEL SYSTEM— GASOLINE ENGINES
Figure 2 9 — Accelerator Pum p Adjustment
(305C, 305E, and 351C Engines)
straight-edge to top of pump piston rod. Open throt­
tle valve and measure distance from straight-edge
to top of pump piston rod.
Subtract the measurement taken with throttle
valve fully closed from measurement taken with
the throttle valve fully open to determine the pump
rod travel. Adjust the pump rod travel by bending
the pump rod at point shown in figure 29.
CONTROL SYSTEMS
IMPORTANT: All gasoline engines, covered
by this manual, sold in the state of Californis are
equipped with C.C.S.-M. (V6 engines) and A.I.R.
(In-Line Engines).
POSITIVE CRANKCASE VENTILATION
SYSTEMS
For detailed information on Crankcase Venti­
lation System s, refer to GASOLINE ENGINES
(SEC. 6A) of this manual.
CONTROLLED COMBUSTION
SYSTEM -M O D IFIED (C.C.S.-M.)
NOTE: The C.C.S.-M. system is found only on
V6 engines, covered by this manual, sold in the
State of California.
Sec. 6M
Page 337