E N G IN E FUEL
6 M -1 1
during the off-idle range they change to fuel mixture
feeds.
Both the idle and off-idle ports are designed to provide a
smooth transition between idling and cruising speeds of
25 to 40 mph for passenger cars, depending on
carburetor design. At these speeds, the throttle opening
and air low are sufficient to permit the main metering
system to begin to supply fuel.
The point at which fuel flow starts from the main nozzle
is the transfer point (Fig. 16). This means that the
carburetor is passing from idle to main metering system.
The idle port discharge however, does not cease at this
point but rather diminishes as main nozzle discharge
increases. Thus, the two systems interact and produce a
smooth fuel-air flow at all engine speeds.
Main Metering System
(Fig. 17)
The main metering system controls the economy range
of the carburetor. It consists of a main jet, main well and
main nozzle with air bleeds in it. The main jet is a very
accurately machined orifice, which controls the fuel flow
through the main well in which the nozzle is located. An
air bleed in the main well and the air bleeds in the main
nozzle keep the mixture constant throughout the
operating range of the main metering system.
As the throttle valve is opened, air velocity through the
venturi system increases which in turn decreases the
pressure in the venturi at the main fuel nozzle. This
action causes the fuel to pass through the main metering
jet into the main well where it rises in the main well
passage and idle pickup tube. As the fuel enters the
nozzle, it is mixed with air through calibrated holes in
the nozzle. Air is bled into the main well by the air
bleeds. This air aids in breaking up the fuel for
improved distribution. The mixture continues through
the main discharge nozzle and enters the air stream at
the boost venturi. At this point it is mixed with the
incoming air and is carried past the throttle valve and
into the manifold for distribution to the engine
cylinders.
TOP AIR BLEED
TUBE TO
E.G.R * VALVE
AIR INLET
Bl— METAL
STRIP
VALVE
HOT IDLE
COMPENSATOR
GASKET
THROTTLE VALVE
IDLE DISCHARGE HOLE
E.G.R. (EXHAUST GAS
RECIRCULATION)
IDLE CHANNEL
RESTRICTION
IDLE TUBE
M AIN METERING JET
TIMED VACUUM
PORT FOR E.G.R. *
OFF— IDLE
PORT
IDLE MIXTURE NEEDLE
ID LE S Y S T E M
OFF— IDLE
OPERATION
Fig. 15—Idle System
LIGHT DUTY TRUCK SERVICE MANUAL
Summary of Contents for Light Duty Truck 1973
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Page 53: ...HEATER AND AIR CONDITIONING 1A 27 LIGHT DUTY TRUCK SERVICE MANUAL...
Page 115: ...LIGHT DUTY TRUCK SERVICE M A N U A L HEATER AND AIR CONDITIONING 1A 89...
Page 123: ...BODY 1B 3 Fig 6 Typical 06 Van LIGHT DUTY TRUCK SERVICE MANUAL...
Page 149: ...BODY 1B 29 Fig 84 Body Mounting 06 Fig 85 Body Mounting 14 LIGHT DUTY TRUCK SERVICE MANUAL...
Page 171: ...LIGHT DUTY TRUCK SERVICE M A N U A L Fig 2 Frame Horizontal Checking Typical FRAME 2 3...
Page 173: ...LIGHT DUTY TRUCK SERVICE M A N U A L Fig 4 10 30 Series Truck Frame FRAME 2 5...
Page 174: ...2 6 FRAME LIGHT DUTY TRUCK SERVICE MANUAL Fig 5 Underbody Reference Points G Van...
Page 185: ...FRONT SUSPENSION 3 11 Fig 16 Toe out on Turns LIGHT DUTY TRUCK SERVICE MANUAL...
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Page 351: ...ENGINE 6 15 Fig ID Sectional View of Eight Cylinder Engine LIGHT DUTY TRUCK SERVICE MANUAL...
Page 375: ...EN G IN E 6 39 LIGHT DUTY TRUCK SERVICE MANUAL...
Page 376: ...6 4 0 ENGINE LIGHT DUTY TRUCK SERVICE MANUAL...
Page 377: ...ENG IN E 6 41 LIGHT DUTY TRUCK SERVICE MANUAL...
Page 378: ...LIGHT DUTY TRUCK SERVICE MANUAL Fig 37L K Series Engine Front Mount 6 42 ENG INE...
Page 400: ...6 6 4 ENG INE LIGHT DUTY TRUCK SERVICE MANUAL...
Page 401: ...ENG IN E 6 65 LIGHT DUTY TRUCK SERVICE MANUAL...
Page 402: ...6 6 6 ENGINE LIGHT DUTY TRUCK SERVICE MANUAL...
Page 403: ...E NG IN E 6 67 Fig 36V C Series Engine Mounts LIGHT DUTY TRUCK SERVICE MANUAL...
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Page 423: ...EN G IN E C OOLING 6K 13 Fig 16 Overheating Chart LIGHT DUTY TRUCK SERVICE MANUAL...
Page 424: ...6 K 1 4 ENG INE COOLING Fig 17 Coolant Loss Chart LIGHT DUTY TRUCK SERVICE MANUAL...
Page 456: ...6M 32 ENGINE FUEL Fig K15 Accelerator Controls G Van L 6 LIGHT DUTY TRUCK SERVICE MANUAL...
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Page 512: ...Fig 18e Vacuum Advance Diagram V8 Engine...
Page 516: ...6 T 2 4 E M IS S IO N CONTROL SYSTEMS LIGHT DUTY TRUCK SERVICE MANUAL...
Page 528: ......
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Page 593: ...CLUTCHES MANUAL TRANSMISSIONS 7M 3 LIGHT DUTY TRUCK SERVICE MANUAL...
Page 598: ...7M 8 CLUTCHES MANUAL TRANSMISSIONS LIGHT DUTY TRUCK SERVICE MANUAL...
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Page 743: ...FUEL TANKS AND EXHAUST 8 13 LIGHT DUTY TRUCK SERVICE MANUAL...
Page 744: ...8 14 FUEL TANKS AND EXHAUST LIGHT DUTY TRUCK SERVICE MANUAL...
Page 760: ...8 30 FUEL TANKS AND EXHAUST Fig 40 Exhaust Pipe P Models LIGHT DUTY TRUCK SERVICE MANUAL...
Page 761: ...FUEL TANKS AND EXHAUST 8 31 LIGHT DUTY TRUCK SERVICE MANUAL...
Page 763: ...FUEL TANKS AND EXHAUST 8 33 LIGHT DUTY TRUCK SERVICE MANUAL...
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Page 832: ...LIGHT DUTY TRUCK SERVICE MANUAL Fig 106 Power Steering Pump Mounting Typical 9 66 STEERING...
Page 833: ...PUMP ASSEMBLY STEERING GEAR TYPICAL SMALL V8 TYPICAL LARGE V8 STEERING 9 67...
Page 861: ...STEERING 9 95 Fig 134 Power Steering Pump Leakage LIGHT DUTY TRUCK SERVICE MANUAL...
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Page 886: ...11 10 CHASSIS SHEET METAL LIGHT DUTY TRUCK SERVICE MANUAL...
Page 891: ...ELECTRICAL BODY AND CHASSIS 12 5 LIGHT DUTY TRUCK SERVICE MANUAL...
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