Chevrolet 1977 light duty truck, Service Manual

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blade to reach full open position. (Start timer when
engine starts).
7. If the choke blade fails to open fully within 3-1/
2 minutes proceed with steps 8-9-10 below.
8. Check voltage at the choke heater connection.
(Engine must be running). If the voltage is a pprox­
imately 12-15 volts, replace the electric choke unit.
9. If the voltage is low or zero, check all wires and
connections. If the connections at the oil pressure switch
are faulty, the oil w arn in g light will be off with the key
" o n " and engine off. If the fuse is blown, the radio or
turn signal indicator will be inoperative. R epair wires or
replace fuses as required.
10. If step 9 is good, replace oil pressure switch.
N O T E : No gasket is used between the choke cover
an d
the choke h o u sin g due to g ro u n d in g
requirem ents.
R efer to figure 6 C -1 1 for the following adjustments:
• Vacuum Break
•
U nloader
• Idle Speed
Checking Solenoid
1. T u rn on ignition, but do not start engine.
2. O pen throttle to allow solenoid plu nger to
extend.
3. Hold throttle lever wide open, feel end o f
plunger and disconnect wire at solenoid.
4. Plunger should move. Some spring tension
should be felt.
5. If plu nger did not move, back out 1/8 hex screw
(counterclockwise) one full turn and repeat steps 3 and 4.
6. If plunger moves in step 5, connect wire to
solenoid and adjust idle speed.
7. If plunger did not move in step 5 insert test
lam p (1893 bulb or smaller) between solenoid feed wire
and ground.
8. If lam p lights, replace solenoid.
9. If lam p does not light, locate cause o f open
circuit in solenoid feed wire.
Idle Mixture
Idle mixture screw has been preset at the factory
and capped. Do not remove the cap during normal
engine m aintenance.
Before suspecting the c arburetor as the cause o f
poor engine p erfo rm an ce or rough idle, check ignition
system including distributor, timing, spark plugs and
wires. Check air cleaner, evaporative emission system,
E FE System, PCV system, E G R valve and engine
compression. Also inspect intake manifold, vacuum hoses
and connections for leaks and check torques o f
ca rb u re to r m ou n tin g bolts/nuts.
In the case o f m ajor carb u reto r overhaul, throttle
body replacem ent, high idle CO as indicated by state or
local emission inspection, the idle mixture may be
adjusted. A djusting mixture by o th e r th an the following
method m a y violate Federal a n d / o r C alifornia or other
state laws.
Idle M ixtu re A djustm ent
1. Set park in g brake and block drive wheels.
2. Remove air cleaner for access to carburetor, but
keep vacuum hoses connected.
3. Disconnect and plug other hoses as directed on
Emission Control In form ation Label u nder the hood.
4. Engine must be at norm al operating te m p e ra ­
ture, choke open, air conditioning off.
5. Connect an ACCURATE tachom eter to engine.
6. Disconnect vacuum advance and plug hose.
Check ignition timing. If necessary, adjust to specifica­
tion shown on Emission Control In form ation Label.
Reconnect vacuum advance.
7. Carefully remove cap from idle mixture screw.
Be careful not to bend screw. Lightly seat screw, then
back out just enough so engine will run.
8. Place transm ission in Drive (automatics with
light duty emissions) or Neutral (all m anuals and
automatics with heavy duty emissions).
9. Back screw out (richen) 1/8 turn at a time until
m axim um idle speed is obtained. T hen set idle speed to
value shown in C hart Column A o f specifications. Repeat
Step 9 to be certain you have m axim um idle speed.
10. T urn screw in (lean) with 1/8 turn increments
until idle speed reaches value shown in C h a rt Column B
o f specifications.
11. Reset idle speed to specification shown on
Emission Control In form ation Label.
12. Check and adjust fast idle as described on the
Emission Control Inform ation Label.
13. Reconnect vacuum hoses. Install air cleaner.
IN S U L A T O R
T O R Q U E S E Q U E N C E
N U T S T O 3 6 IN . LBS.
T O 18 F T . LBS.
i I •'
T IG H T E N
. . .T H E N
H E A T S T O V E