There is also a third secondary style. It's not used on Holleys
but it is popular on Carter and Rochester 4 bbls. It consists of
a mechanical secondary linkage plus a spring loaded or weighted
flapper door located directly above the secondary throtle plates.
Looks a little like a choke plate over the secondaries. The mechanical
linkage opens the throttle plates but the flapper restricts flow until
airspeed is sufficient to support the additional fuel. The Thermoquad
used this arrangement with a shaped flapper that provides a pseudo
variable venturi effect. Rochester Quadrajets, Carter AVS's and
Thermoquads use an adjustable spring loaded set up. I believe the
Motorcraft 4300D spreadbore used something similar. Carter AFB's
and their Edelbrock clones use a weighted arrangement. Not applicable
to your Holley, just a bit of trivia.
Dan Jones
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There are, to my limited knowledge, two types of 4 barrels. The
mechanically operated secondaries, which are activated by external
levers and slotted plates that open them at a set opening of the
primaries at a rate set by the geometry of the linkages. These linkages
are primarily on the left side of the carb.
The other is a vacuum operated secondary system. On the Holley, (which
Ford has sometimes used with their label on it), there is a vacuum
operated diaphragm/draw-bar on the right rear side of the carb. It has
a large flat top, covering a rubber diaphragm, and has replaceable rate
control springs, seals, and check valves to open the secondaries when
the engine air-flow demands require more. These are adjustable through
spring selection.
Do either of these sound like yours?
Steve
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
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