of the carburetor, controls the throttle plates in
the usual manner. When governing speed is
reached, a combination of venturi and manifold
vacuum acts on the governor diaphragm to close
the throttle plates. Two calibrated by-pass jets
in the vacuum passages meter the vacuum from
the venturi and the manifold to provide the correct
balance for proper operation of the governor. At
speeds below governing rpm, this vacuum is
weakened by air bleeding through the governor
valve so that no premature governing action will
occur. Filtered air from the carburetor air
cleaner enters the governor system through the
governor vent tube. The air flows through an air
line to the housing enclosing the governor rotor.
A combination of low pressure from the venturi
and manifold transmitted through the governor
system passages, draws the air past the governor
valve and through another air line to the throttle
actuating unit on the carburetor. In the controlling
unit, centrifugal force acting on the rotor, which
has kept pace with engine speed, overcomes the
tension of the valve spring and tends to close the
governor valve when governing speed is reached.
This greatly restricts the amount of air bleeding
through to the diaphragm on the carburetor, thus
allowing the combined venturi and manifold pres
sure differential to operate the diaphragm.
As the pressure differential across the dia
phragm increases, the diaphragm moves the
governor lever against the tension of the governor
spring to close the throttle plates. The governed
engine speed is held for constant load by centri
fugal force on the valve balanced against the tension
of the valve spring. Any slight change in engine
speed due to load restriction will cause the gov
ernor valve to react immediately, either increas
ing or decreasing the amount of air bleeding
through the governor valve orifice. A change in
the amount of air bleed will, in turn, cause an
instant response from the diaphragm to increase
or decrease the throttle plate opening.
accelerator is released, control is taken from the
governor by the external throttle lever and the
return spring in the accelerator pedal linkage
closes the throttle plates to bring the engine to
any desired lower speed.
Although the entire governor system is de
scribed, only the throttle actuating mechanism
on the carburetor is included in theoverhaulpro
cedure presented in this manual. This portion of
the governor can be cleaned and serviced readily,
also the governor rotor can be serviced independly.
See Holley Manual B-183 for servicing of governor
The approved method for properly overhauling
a carburetor calls for the complete disassembling.
A thorough cleaning and a careful inspection of
each part is essential. Defective parts should
be replaced with genuine Holley replacement parts
and the carburetor should be carefully rebuilt.
Care in rebuilding and accuracy in adjusting the
carburetor will insure the same top quality per
formance engineered into every Holley Carburetor.
2. SPECIAL TOOLS
MASTER REPAIR KITS
The overhaul procedure which follows can be
accomplished with ordinary tools if a reasonable
amount of care is exercised.
approved tools are recommended to facilitate
overhaul and to prevent damaging of vital parts.
The special tools recommended for use in
the overhaul of these carburetors are listed above:
Master Repair Kits contain Holley replace
ments for parts which are subject to wear or may
be damaged in disassembly. The disassembly
procedure includes instructions to discard all
gasket and parts which have replacements in the
Master Repair Kits. The proper kit for each
carburetor is listed in the current Holley Carbu
retor Parts Catalog.