|
ROCHESTER CARBURETORS Bulletin 9D-9 January 1952 |
|||
|
Page 6
ROCHESTER PRODUCTS, DIVISION OF GENERAL MOTORS,
ROCHESTER, NEW YORK |
|||
|
|
|||
|
PART THROTTLE SYSTEM
|
|||
|
|
|||
|
|
|||
|
Figure 7-2 |
|||
|
|
|||
|
As the
throttle valves are opened to a greater degree and more air is drawn through the carburetor, it is
necessary to provide means, other than the idle systems, for supplying additional fuel to meet
the engine requirements.
Use Figure 7-2 as a
reference.
The primary
or pump side of the carburetor meets this increased demand for fuel in the
following manner: At a
point of sufficient throttle opening, manifold vacuum or suction,
multiplied several times in [he primary (1) and secondary Venturi (2). is transmitted
to Che tip of the main well tubes or main discharge
nozzles (3). This suction draws fuel from the float bowl,
through the calibrated main
metering jets (4) and into the
air bled main well lubes (5). After passing through the main well tubes (5) air joins the
mixture at the main well bleeds
(6). The mixture then passes from the
tip of the nozzle through the Mixture Passage
(7), to the secondary Venturi (2) and on into the intake manifold. As the throttle opening is progressively increased and
more fuel is drawn through the
main well tubes, the fuel
level in the main wells drops. As this fuel level drops, the calibrated holes in the main well
tubes become uncovered of
fuel. When this occurs, thev be- |
come air bleeds, thus mixing
progressively more air with the fuel passing through the main well
tubes. Thus although the nozzle suction is increased by
in-creasing the throttle opening, the fuel mixture to the engine remains
constant throughout the Part Throttle range.
As throttle opening increases.
lower idle air bleeds (8) which now become part throttle
feed nozzles have been placed in the main air flow channels below the
primer Venturi (1). These
nozzles, being exposed to manifold vacuum during part throttle operation,
draw fuel through both the Primary and Secondary idle systems as
described on the previous page. It will he noted that these nozzles acted
as air bleeds during the operation of the idle system. Now they arc acting as
discharge
nozzles.
The throttle valves on the
secondary or fuel inlet side of [he carburetor do not open until the
primary linkages engage the
secondary throttle shaft. They must then open fully during the remaining few degrees of primary
throttle travel. The secondary
side, therefore, only supplies fuel
in the idle and power ranges. The part throttle or intermediate
range is controlled completely on the primary side of the
carburetor. |
||
|
|
|||
