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FUEL SYSTEM
6C-5 1
Fig. 6C-91A M4MC Carb 350
X
Series VI Code
L
INLET N U T
f-x
INLET
GASKET
* , I
c - -
SPRING
Fig. 6C-92 Fuel Filter
break system is used on most models for improved cold
engine warm-up and drive-away performance. The choke
shaft and certain other parts of the choke system are Teflon
coated to insure smooth choke operation.
The carburetor part number is stamped on a vertical
section of the float bowl, near the secondary throttle lever
(Fig. 6C-93). Refer to the part number on the bowl when
servicing the carburetor. When replacing the float bowl
assembly, follow the instructions contained in the service
package. Stamp or engrave the model number on the new
float bowl.
The primary side of the carburtor has six systems of
operation. They are float, idle, main metering, power, pump
and choke. The secondary side has one metering system
which supplements the primary main metering system and
receives fuel from a common float chamber. (See Figs. 6C-94
thru 6C-101).
DIAGNOSIS
Refer to engine performance diagnosis, Section 6, and/or
cleaning and inspection under unit overhaul in this section.
ON-CAR SERVICE
Carburetor Choke and Hoses
Check choke mechanism and vacuum break for proper
operation at the recommended maintenance intervals. Any
binding condition which may have developed due to
petroleum gum formation on the choke shaft or from damage
should be corrected. Check carburetor choke hoses for proper
connection, cracking, abrasion or deterioration and correct
or replace as necessary.
Choke Check Procedure
1. Remove air cleaner. With engine off, hold throttle half
open. Open and close choke several times. Watch linkage to
be certain all links are connected and there are no signs of
damage.
2. If choke or linkage binds, sticks or works sluggishly,
clean with United Delco Choke Cleaner X-20-A or
equivalent. Use cleaner as directed on can. If cleaning does
not correct, replace binding parts.
3. Visually inspect carburetor to be certain all vacuum
hoses are connected. Inspect hoses for cracks, abrasion,
hardness or signs of deterioration. Replace or correct as
necessary.
4. Make sure vacuum break diaphragm shafts are fully
extended when engine is off. If shafts are not fully extended,
replace vacuum break assembly. Start engine, primary
vacuum break diaphragm shaft should fully retract. If unit
fails to retract, replace vacuum break assembly.
5. With engine at normal operating temperature, the
SVB TVS must be open. Check by applying either engine
vacuum or auxiliary vacuum to the inlet port on hot TVS and
checking for vacuum at the outlet. If there is no vacuum,
replace the TVS.
6. Apply a vacuum to the vacuumbreak diaphragm and
observe for movement to the full travel position. Due to the
orifice in the unit, it will take up to 20 seconds to reach full
travel. If full travel is not obtained, the orifice is plugged and
the diaphragm must be replaced.
ADJUSTMENTS
Idle Speed Adjustment
Refer to Vehicle Emission Control Information label on
vehicle for latest certified specification information.
1. With engine at normal operating temperature, choke
full open, and air conditioning OFF, connect a tachometer
to engine.
2. Set parking brake and block drive wheels.
3. Disconnect and plug hoses from vapor canister and
EGR valve.
4. Turn A/C off.
5. Start engine and position transmission in PARK or
NEUTRAL.
6. Disconnect vacuum advance line.
7.
Check and adjust engine timing at specified rpm
8. Reconnect vacuum advance line.
9. Place transmission in drive (automatic) or neutral
(standard transmission) and adjust idle speed.
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