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OPERATION
The fuel-air mixture requirements of
an
automotive engine vary considerably
throughout
its range of operation.
To provide the correct
mixture during all phases of operation,
the Holley
Carburetor Model 1901 is equipped
with four basic
fuel metering systems. They are the
main meter
ing system, the idle system, the power
enrichment
system and the accelerating pump system.
These
four systems are calibrated to deliver
an economi
cal mixture for normal cruising conditions,
a
richer mixture when high power output
is desired,
and a still richer mixture for smooth
idle and low
speed performance.
In addition, there is a fuel inlet
system which
provides the four basic metering systems
with a
constant supply of fuel, and a choke
system which
provides a means of temporarily enriching
the
mixture to aid in starting and running
a cold engine.
When the engine is running, differences
in air
pressure within the carburetor cause
the proper
discharge of fuel for the various
engine speed and
load conditions, as explained in the
following para
graphs. In the explanation of the
basic fuel meter
ing systems, the air in the carburetor
float chamber
will be considered as being at normal
atmospheric
pressure. It may actually be at a
pressure very
slightly less than atmospheric, due
to the restric
tion to the air flow through the air
cleaner. How
ever, to simplify the explanation
of the function of
the fuel metering systems, this factor
will be
disregarded and the pressure will
be considered
as being atmospheric.
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