Chevrolet Light Duty Truck 1973 Service Manual page 441

clogged carburetor or fuel pump filter may restrict fuel
flow or bypass foreign m aterial into carburetor
depending upon type used. Replace clogged filters. Also
replace filters each
12,000
occurs first.
CEC VALVE, OR VACUUM ADVANCE SOLE­
NOID, AND HOSES-The vacuum portion of either of
these valves should be checked, with the transmission in
neutral, by using a vacuum gauge attached to the valve
(or solenoid) distributor connector. With the engine at
fast idle, the vacuum gauge should read zero. The
electrical portion of the solenoid or valve may be
checked by applying
12
terminals, which should result in a vacuum reading on
the gauge — a vacuum reading should be obtained only
while the solenoid or valve is not energized. An
inoperative or leaking solenoid or valve should be
replaced.
All hoses and wires should be carefully inspected for
correct routing and to make certain that they are intact.
EXTERNAL ADJUSTMENTS (ALL CARBURETORS)
Adjustments........................................................................ 6M-17
Removal .............................................................................. 6M-23
Test Before Installation ..................................................... 6M-24
Installation ........................................................................... 6M-24
ROCHESTER MV, 2GV AND 4 M V ADJUSTMENTS
FAST IDLE ADJUSTMENTS (Figs. 1C, 2C
and
3C) ROCHESTER MV AND 4MV
NOTE: The fast idle adjustment must be set
with transmission in "N eutral."
1. Position fast idle lever on high step of fast idle
cam.
2. Be sure choke is properly adjusted and in wide open
position - engine warm.
3. Set fast idle to specified rpm as follows:
a. Adjust fast idle screw on Rochester 4MV (Fig.
2C).
b. Bend fast idle lever as required on Rochester
MV to specified speed (Fig. 1C).
FAST IDLE ADJUSTMENT-ALL 2 BBL.
NOTE: The two barrel carburetors are preset
miles or months, whichever
12
volts across its electrical
IDLE STOP SOLENOID-The idle stop solenoid
should be checked to assure that it permits the throttle
plate to close further when the ignition switch is turned
"off." An inoperative solenoid should be replaced.
PRELIMINARY CHECKS (ALL
CARBURETORS)
1. Thoroughly warm-up engine. If the engine is cold,
allow to run for at least 15 minutes.
2. Inspect torque of carburetor to intake manifold
bolts and intake manifold to cylinder head bolts to
exclude the possibility of air leaks.
3. Inspect manifold heat control valve (if used) for
freedom of action and correct spring tension.
4. Check and adjust choke as required, using
procedures specified in this section.
5. Adjust idle speed and idle mixture as outlined in
Section , "Engine Tune-up" and at the end of the
6
carburetor group in this section under, "Additional
External Settings and Adjustments."
INDEX
Fuel Filter M aintenance........................................... 6M-25
Automatic Choke Coil Assemblies....................... 6M-25
Choke Coil R eplacem ent.......................................... 6M-25
Additional External Settings and Adjustments. 6M-26
Throttle Linkage Adjustm ent.................................. 6M-27
to the approximate fast idle RPM noted in
specifications, listed under "Fast Idle (Run­
ning) RPM adjustment", when low step idle
is set. (Also note Low Idle RPM in
specifications).
CHOKE ROD (FAST IDLE CAM)
ADJUSTMENTS MV (Fig. 4C)
NOTE: Make sure that the fast idle
adjustment is made previous to choke rod
adjustment.
Automatic choke models with steps on fast idle cam.
W ith fast idle adjustment made:
1. Place fast idle cam follower on second step of the
fast idle cam and hold firmly against the rise to the
high step.
E N G IN E FUEL 6 M - 1 7
LIGHT DUTY TRUCK SERVICE MANUAL