Stihl 064 Service Manual page 77

STIHL 064, 066
11.2 Construction and
Operation of Carburetor
with Compensator
Carburetor without compensator
Pi = Internal pressure
Pa = Atmospheric pressure
Pr = Pressure in metering chamber
1 = Box-type filter
The compensator carburetor
keeps the fuel content in the
mixture constant at all times,
irrespective of how dirty the air
filter is. The pressures at the
clean air side of the air filter
and the metering diaphragm are
always equal.
The end cover of the new carbure-
tor, the rear half of the air filter
each have an integrally molded
connector.
Carburetor with compensator
Pi = Internal pressure
Pa = Atmospheric pressure
Pr = Pressure in metering chamber
1 = Compensator
2 = Box-type filter
A sleeve is fitted between the end
cover and air filter.
The air volume is reduced when
the air filter is dirty. This not only
increases the depression in the
carburetor's venturi, but also de-
creases the pressure applied to
the outside of the metering dia-
phragm. The metering diaphragm
moves upward, causing the
needle valve to close part-way and
thus reduce the supply of fuel.
The mixture cannot become over-
rich. And it is no longer necessary
to alter the setting of the high
speed adjusting screw as contami-
nation of the air filter increases.
However, engine performance
drops due to the reduction in air
volume and can only be restored
to normal by cleaning the air filter.
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