Chevrolet 70 Series 1970, Service Manual

Page: 509 / 841

ENGINE FUEL SYSTEM 6M-16
le v e r next to float to change the float setting . Use
bending tool a s illu s tra te d in figure 11.
A fter checking the float level, in stall a i r horn
and a new g asket. Locate sc re w s, choke control
b ra c k e t, and identification tag in o riginal positions.
Connect fa st idle link, ac celeratin g pump rod, and
choke w ire . In stall a i r clea n er.
EXHAUST EMISSION
Since products of com bustion in gasoline en­
gines contain contam inants which cause atm o s­
p h e ric pollution, a m eans to reduce harm ful e m is­
sions m ust be employed. D evices u sed fo r this
pu rp o se fall into one of the following categ o ries:
1. P o sitiv e C rankcase V entilation System
(P.C .V .).
2. C ontrolled Com bustion System - Modified
(C .C.S.-M .).
The f ir s t sy stem s e rv e s to p rev ent a ir pollu­
tion by re -c y c lin g fum es fro m the cran k ca se (used
on all engines). The o th er sy ste m is u sed fo r con­
tr o l of a i r pollution fro m exhaust sy stem . A ll g a s­
oline engines covered by th is manual, a r e equipped
with C .C .S.-M .
POSITIVE CRANKCASE VENTILATION
SYSTEMS
F o r detailed inform ation on C ran kcase Vent­
ilatio n S ystem s, r e f e r to GASOLINE ENGINES
(SEC. 6A) of th is m anual.
CONTROLLED COMBUSTION
SYSTEM MODIFIED (C.C.S.-M.)
The C .C .S.-M . sy ste m is that sy stem which
in c re a s e s com bustion efficiency, and com bustion
efficiency reduces the hydrocarbon and carbon
monoxide em issio n s. The com plete effectiveness
of this sy stem , a s well a s full power and p e rfo rm ­
ance, is dependent upon the c o rre c t idle speed,
ignition tim ing, and idle fuel m ixture.
IMPORTANT: The C .C .S.-M . sy stem co n sists
of no additional com ponents, o th er than a specially
c a lib ra te d c a rb u re to r and a vacuum idle stop.
CARBURETOR
The c a rb u re to r used on C.C .S.-M . equipped
veh icles functions and o p erates the sam e a s all
o th er B endix-S trom berg c a rb u re to rs used on V6
engines. But u n d er no circu m stan ces should they
be interchanged with, o r rep laced by another type
c a rb u re to r.
ACCELERATOR PUMP TRAVEL ADJUSTMENT
M easure the total d istance from the point at
top of pump le v e r tra v e l when th ro ttle le v e r is
moved fro m closed to wide open position a s shown
in fig u re 12. The pump tra v e l is as indicated in
"S p ecification s.” When n e c e ssa ry to ad just the
le v e r tra v e l, bend the pump ro d at the upper end.
CONTROL SYSTEMS
NOTE: F o r c a rb u re to r adjustm ents on C.C.S.
-M . engines, re fe r to "Idle and M ixture A djust­
m en ts" p rev iou sly covered in th is section.
VACUUM IDLE STOP (R efer to Fig. 13)
A vacuum idle stop unit is u sed on a ll C.C.S.
-M . equipped engines to prev en t engine " d ie s e l-
ing” (engine operation a fte r ignition sw itch is
tu rn ed off).
The idle stop unit is mounted to the c a rb u r­
eto r with a b rack et and a c ts upon the th ro ttle plates
of the c a rb u re to r in the sam e m anner a s an idle
se tsc re w . When the engine is s ta rte d , engine vac­
uum a c ts upon the diaphragm in the idle stop unit
and the plunger is pushed to its full extended p o si­
tion. The plunger ac ts upon the th ro ttle le v e r and
s e ts the th ro ttle p lates in a position to achieve the
specified idle rp m . When the ignition sw itch is
tu rn ed ''O F F ,” engine vacuum is red uced and the
plung er r e tr a c ts into the idle stop unit. The re su lt
is the th ro ttle p late clo ses to a low er position
Figure 13—Vacuum
Idle Stop Installation
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL