Chevrolet Light Duty Truck 1973, Service Manual

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E N G I N E FUEL 6 M - 1
SECTION 6M
ENGINE FUEL
CONTENTS OF THIS SECTION
Description......................................................................... 6M-1
Theory of Operation...................................................... 6M-3
Maintenance and Adjustments................................... 6M-16
Service Operations........................................................... 6M-23
Diagnosis............................................................................ 6M-42
Special Tools..................................................................... 6M-67
DESCRIPTION
This Section of the 1973 Truck Service Manual covers the
above "Contents" items as they relate to carburetors and
the engine fuel system. This service section also includes,
carburetor removal and installation and external
adjustments for all 10-30 series trucks, in addition to,
maintenance procedures for choke coils, throttle linkage,
accelerator and choke controls, air cleaners and fuel
filters. For carburetor identification, overhaul procedures,
assembly and disassembly of components, and internal
carburetor adjustments, refer to Section 6M, of the
Overhaul Manual, under the carburetor being serviced.
In addition to carburetor adjustment specifications, also
refer to Specifications at the end of the manual for
carburetor application and type.
Carburetors used with 10-30 Trucks are designed to
meet the particular requirements of engine, transmission
and vehicles. Carburetors that look alike are not always
interchangeable. (Refer to carburetor part number and/
or specifications). Service procedures for the various
carburetors are similar, therefore, typical illustrations
and procedures are used except where specific illustra­
tions or procedures are necessary to clarify the
operation.
MODEL MV (lbbl.) CARBURETOR
The Model MV carburetor is a single bore down-draft
carburetor using a triple venturi in conjunction with a
plain tube nozzle.
Fuel flow through the main metering system is controlled
by a main well air bleed and fixed orifice jet. The power
enrichment system is used to provide good performance
during moderate to heavy accelerations.
The idle system on automatic transmission models
incorporate a hot idle compensator to maintain smooth
engine idle during periods of extreme hot engine
operation.
The Model MV carburetor has an automatic choke
system. The vacuum diaphragm unit is mounted
externally on the air horn. The choke coil is mounted on
the manifold and is connected to the choke valve shaft
by a rod.
An integral fuel inlet filter is mounted in the fuel bowl
behind the fuel inlet nut to give maximum filtration of
incoming fuel.
Other features of the Model MV include an aluminum
throttle body, and a thick throttle body to bowl insulator
gasket. The carburetor has internally balanced venting
through a vent hole in the air horn, which leads from the
bowl into the bore beneath the air cleaner.
The carburetor model identification is stamped on a
vertical portion of the float bowl adjacent to the fuel
inlet nut. If replacing the float bowl, follow the
instructions contained in the service package to transfer
the identification.
An electrically operated idle stop solenoid is used on all
MV models. The solenoid mounts on the carburetor float
bowl and replaces the normal carburetor idle stop screw.
The curb idle speed setting is made by turning the
electrically operated idle stop solenoid in the boss located
on the carburetor bowl. See "Idle Stop Solenoid
Adjustment".
In the manual transmission models, the idle stop
solenoid is used along with a Combination Emission
Control (C.E.C.) valve. The C.E.C. valve, when energized
through the transmission, acts as a throttle stop by
increasing idle speed during high gear deceleration and
helps in controlling overrun hydrocarbons. The C.E.C.
valve also provides full spark vacuum advance to the
distributor during high gear operation and is de­
energized in lower gears and at idle for retarded spark
timing during this period.
The idle mixture screw has a limiter cap installed and no
adjustment will be provided on the vehicle. The mixture
screw is pre-set at factory and capped and no further
adjustment is required.
An Exhaust Gas Recirculation system (E.G.R.) is used on
all applications for 1973 to control oxides of nitrogen.
The vacuum supply port necessary to operate the
recirculation valve is located in the throttle body and
connects through a channel to a tube which is located at
the top of the air horn casting. See Idle System for port
location and operation.
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LIGHT DUTY TRUCK SERVICE MANUAL