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MAXIMUM POWER
When the throttle is
wide open, the carburetor is supplying all possible
air. Since no further air is available, the
only way to increase power is to make certain
that all the incoming air is used for combustion.
In spite of the best
efforts of designers, perfect distribution is
never reached; the average mixture supplied
to an engine may be completely correct, but
some cylinders will run slightly rich and others
slightly lean. So with no more air available
through the carburetor, the lean cylinders are
the only source of unburned air. The mixture
supplied to the engine is richened until the
lean cylinders become normal and all possible
air is used for combustion. Of course, the already
rich cylinders will be made slightly richer,
but the excess fuel simply travels out with
the exhaust gases.
Now it can be seen that
for maximum power, extra fuel is added to use
all available air and fuel economy becomes secondary.
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FUEL ECONOMY
For operation other
than maximum power, it is desirable to supply
an air-fuel mixture for maximum economy. Economy
requires the reverse of maximum power, in that
enough air is added to insure the use of all
available fuel, so that no fuel will leave the
engine unburned. The majority of driving conditions
allow an economy mixture, but in some cases
economy must take a back seat to power. So the
automotive carburetor must be able to supply
either mixture to the engine, according to power
demands.
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