GMC 1976 ZEO 6083 Maintenance Manual page 11

0- 1 0
GENERAL INFORMATION
EMISSION CONTROL
MAINTENANCE
(1975 - 1976 CERTIFIED ENGINE)
35 THERMOSTATICALLY
CONTROLLED AIR
CLEANER-Inspect installation to make certain that
all hoses and ducts are connected and correctly in-
stalled. Also cheek valve for proper operation.
36 CARBURETOR
CHOKE AND HOSES-Check
choke mechanism for free operation . Any binding
condition which may have developed due to pe
troleum gum formation on the choke shaft or from
damage should be corrected.
Check carburetor
choke hoses for proper connection, cracking, abra-
sion or deterioration and correct or replace as neces-
sary.
37 ENGINE IDLE SPEED AND MIXTURE-Adjust en-
gine idle speed accurately (following the specifica-
tions shown on the label attached to the engine
rocker cover) at the first 6 months or 6,000 miles of
operation, then at 12 month or 12,000 mile intervals.
Adjustment must be made with test equipment
known to be accurate .
At 12 month or 12,000 mile intervals or in case
of major carburetor overhaul, or when poor idle
quality exists, the idle mixture should be adjusted by
use of a CO meter when an accurate meter is availa-
ble, or the alternate mechanical method (lean drop)
should be used to adjust the idle mixture. (See Sec-
tion 6M).
38 CARBURETOR AND INTAKE MANIFOLD MOUNT-
ING-Torque carburetor and intake manifold attach-
ing bolts and/or nuts at first 6 months or 6,000 miles
-then at 12 month/ 12,000 mile intervals.
39 SPARK PLUGS-Replace at 6,000 mile intervals
when operating with leaded fuels, or at 12,000-mile
intervals when using unleaded fuels. Use of leaded
fuels results in lead deposits on spark plugs and can
cause misfiring at mileages less than 12,000 miles.
Where misfiring occurs prior to 6,000 miles, spark
plugs in good condition can often be cleaned, tested,
and reinstalled in an engine with acceptable results.
40 CARBURETOR FUEL FILTER-Replace filter at
12-month 12,000-mile intervals or more frequently if
clogged.
41 THERMAL VACUUM SWITCH AND HOSES-
Check for proper operation.
A malfunctioning
switch must be replaced . Check hoses for proper
connection, cracking, abrasion or deterioration and
replace as necessary.
42 POSITIVE CRANKCASE VENTILATION SYSTEM
(PCV}-Check the PCV system for satisfactory operat-
ion at 12,000-mile intervals, and clean filter (located
in rocker cover) . Replace the PCV valve at 24,000-
mile intervals and blow out PCV valve hose with
compressed air. Replace deteriorated hoses.
43 AIR CLEANER ELEMENT-Replace the engine air
cleaner element under normal operating conditions
every 12,000 miles. Operation of vehicle in dusty
areas will necessitate more frequent element replace-
ment . Your GMC MotorHome dealer can be of as-
sistance in determining the proper replacement
frequency for the conditions under which you oper-
ate your vehicle.
CAUTION: DO not operate the engine without the air
cleaner unless temporary removal is necessary during repair
or maintenance of the vehicle. When the air cleaner is
removed back-firing can cause fire in the engine compart-
ment .
44 SPARK PLUG WIRES-Clean exterior of wires;
remove any evidence of corrosion on end terminals.
Inspect spark plug wires for evidence of checking,
burning, or cracking of exterior insulation and tight
fit at distributor cap and spark plugs or other deterio-
ration . If corrosion cannot be removed or other con-
ditions above are noted, replace wire .
45 TIMING AND DISTRIBUTOR CAP-Adjust igni-
tion timing following the specification on label at-
tached to the engine rocker cover.
Also, carefully inspect the interior and exterior of
the distributor cap and rotor for cracks, carbon
tracking and terminal corrosion. Clean or replace as
necessary .
46 THROTTLE RETURN CONTROL (TRC)-(California
Vehicles) Check hoses for cracking, abrasion or
deterioration and replace as necessary. Check system
for proper operation.
47 EVAPORATION CONTROL SYSTEM (EM-Check
all fuel and vapor lines and hoses for proper connec-
tions and correct routing as well as condition.
Remove canister(s) and check for cracks or damage.
Replace damaged or deteriorated parts as necessary.
Replace filter in lower section of canister .
If vehicle is equipped with two canisters, filter is
located in the lower canister only .
48 FUEL CAP, FUEL LINES AND FUEL TANKS-In-
spect the fuel tank cap and lines for damage which
could cause leakage. Inspect fuel cap for correct seal
ing ability and indications of physical damage . Re-
place any damaged or malfunctioning parts.