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FUEL SYSTEM
6C-37
M O D E L M Z M C 200 C A R B U R E T O R
CONTENTS
General Description
.............................................
6C-37
On-Car Service
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6C-38
Adjustments (Overhaul)
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6C-39
GENERAL DESCRIPTION
The model M2MC 200 carburetor for 1977 is a 2-barrel
single stage carburetor of downdraft design (Fig. 6C-63). It
has the proven design features of the primary side of the
M4MC carburetor.
The triple venturi, with small 1-3/8" bores, makes the
model M2MC 200 especially adaptable to smaller engine
sizes. The triple venturi stack up, plus smaller bores, results
in good fuel metering control during all periods of operation.
Fig. 6C-63 M2MC 2 0 0 Carburetor
The main metering system has separate main wells to
feed each main nozzle for good fuel flow through the venturi.
For ease of service, alphabetical code letters are cast in
the air horn, float bowl, and throttle body at external tube
locations to identify air and vacuum hose connections.
An adjustable part throttle screw is used in the float bowl
to aid in refinement of fuel mixtures for good emission
control. This screw is preset at the factory and should not be
adjusted in service. If it becomes necessary to replace the float
bowl, the new service float bowl will include an adjustable
part throttle screw which has been preset at the factory. An
aneroid cavity insert is used in the float bowl.
C A U T I0 N
: The insert is required to reduce fuel
slosh in the float bowl.
During off-idle and part throttle operation, fuel metering
is accomplished by two tapered metering rods, operating in
the main metering jets, positioned by a manifold vacuum
responsive piston. During greater throttle openings when
additional fuel is needed for power, the two rods are
positioned mechanically by a lever operated off the center of
the throttle shaft. The use of both a mechanical and vacuum
enrichment more accurately controls fuel metering during
light and heavy power requirements.
Carburetor Replacement
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6C-40
......................................
Fuel Filter Replacement
6C-40
............................................
Carburetor Overhaul
6C-44
This model uses a plastic float with a windowless type
needle seat for better fuel handling. A plastic filler block is
used above the float chamber to reduce fuel slosh in the float
bowl.
A 2 inch paper fuel filter with check valve is used to shut
off fuel flow to the carburetor and prevent fuel leaks if a car
roll-over should occur.
The carburetor part number is stamped on a vertical
section of the float bowl, near the secondary throttle lever
(Fig. 6C-64).
IDENT.
e
Fig. 6C-64 Identification
Refer to the part number on the bowl when servicing the
carburetor.
There are six basic systems used in the M2MC 200
carburetor: Float, Idle, Main Metering, Power, Pump and
Choke (Figs. 6C-65 thru 70).
The M2MC 200 uses a bowl mounted hot air choke with
a fresh air modulator (Fig. 6C-7 1) and primary and secondary
vacuum breaks. The secondary vacuum break is controlled
by a TVS mounted in the air cleaner. The TVS (Fig. 6C-72)
is closed when carburetor air inlet temperature is below 62°F.
When inlet air temperature is above 62"F., vacuum is applied
to the secondary vacuum break and the choke blade is opened
to a wider position. Refer to On-Car Service in this section
for a functional test of the TVS. Refer to Section 6E, for
vacuum hose connections to the secondary vacuum break
TVS. The fresh air modulator restricts air flow to the choke
coil when the temperature in the air cleaner is below
approximately 60°F. for good cold driveability. Above
approximately 60"F., the air flow is unrestricted and choke
opening is quicker. Refer to On-Car Service in this section
for functional test and replacement procedures of the fresh
air modulator valve.
DIAGNOSIS
Refer to engine performance diagnosis, Section 6, and/or
cleaning and inspection under unit overhaul in this section.
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