6 M - 4 E N G IN E FUEL
METERING
CORRECT P R O P O R TIO N S
O F FUEL A N D AIR
A T O M IZ A T IO N
SPRAY O F FINE PARTICLES
GREAT AIR C O N T A C T
DISTRIBUTION
U N IF O R M MIXTURE
DELIVERED T O M A N IF O L D
Fig. 1 -Basic Functions
ATOMIZATION
The engine’s source of fuel for power is gasoline. Before
gasoline can be used as fuel for an engine, it must be
atomized which means breaking the fuel into fine
particles so that it can be mixed with air to form a
combustible mixture. Contrary to popular belief,
gasoline in its liquid state is not combustible; only
gasoline vapor will burn. A common example of this is a
cigarette lighter which works fine indoors but then can’t
be lit after you’ve been outdoors in the cold for awhile.
At warmer temperatures, fuels vaporize quickly and so
can be ignited easily but at lower temperatures,
evaporation is slower and accordingly ignition is
impossible or, at least, difficult because of insufficient
vapor.
While this analogy is quite simple, it is an illustration of
the basic problems of carburetor design; that is, the
provision of combustible fuel mixtures over a broad
range of temperature and operating conditions. The
complexity of design problems continues to mount each
year due to a constant effort to reduce exhaust emissions
and at the same time improve operating conditions.
To be combustible, gasoline must vaporize. Vaporization
is the act of changing from a liquid to a gas and this
change of state occurs only when the liquid absorbs
enough heat to boil. This is what happens in a tea kettle
to change water to water vapor, or steam. Heat is
transferred to the water, raising its temperature until it
finally reaches the boiling point, at which time the water
changes to steam and is carried off to atmosphere in this
gaseous form. At seal level, the water will oil at 212°F
but at high altitudes, less heat is required for water to
boil due to lower atmospheric pressure. This is known as
the temperature-pressure relationship; that is, as the
pressure is reduced, the boiling point is reduced. This
law, combined with a process known as atomization, has
important applications in the transformation of liquid
gasoline to a capor for use in combustion.
In a carburetor (Fig. 2), gasoline is discharged into the
incoming air stream as a spray and the spray is then
atomized, or torn into fine droplets to form a mist. The
resulting air-fuel mixture is drawn into the intake
manifold. At this point, the change of state occurs and
the fuel "mist" vaporizes as the result of several factors.
Since the pressure in the intake manifold is far less than
atmosphere, the boiling point of the gasoline is lowered
considerably. At this reduced pressure, latent heat
absorbed from the many air particles surrounding each
fuel particle causes some vaporization, which is further
aided by heat on the intake manifold floor.
Because complete fuel vaporization is the result of many
factors (ambient temperature, fuel temperature, mani
fold vacuum, and intake manifold temperature), it is
easy to see that anything which reduces any one of these
factors will adversely effect vaporization and thus reduce
fuel economy and increase exhaust emissions. Some
examples would be cold weather, an inoperative exhaust
heat control valve, and high overlap camshafts and/or
heavy throttle demands. While the effects from lower
temperatures are obvious, reduction of manifold vacuum
either by valve timing or heavy throttle operation are
highly detrimental to fuel economy due to the higher
pressures (and boiling points) resulting in the intake
manifold which reduces the amount of fuel vaporization
which will occur by the time the charge enters the
combustion chamber. Fuel not vaporized at the time of
induction is, to a large extent, exhausted unburned from
the combustion chamber and can cause high hydro
carbon exhaust emissions.
We know that gasoline, for combustion, must be
vaporized or as the change of state can be loosely
considered, absorbed by air. However, this requirement
LIGHT DUTY TRUCK SERVICE MANUAL
Summary of Contents for Light Duty Truck 1973
Page 1: ......
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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...
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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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