ROCHESTER CARBURETORS

Bulletin 9D-98  February 15, 1957

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Rochester Carburetors
BULLETIN 9D 98
PAGE 1 DATE; 2-15-57
REPLACES
9D 98 11-7-52
OPERATION AND MAINTENANCE
OF THE
ROCHESTER IDLE SPEED-UP CONTROL 1954-1957 CADILLAC 4GC
The idle speed-up control mounted on the carburetor is used on air conditioned cars only. The purpose of this unit is to provide full air conditioning efficiency whenever the car is stopped for any length of time. The only time that the idle speed-up control is in operation is when the transmission is in neutral or park position.
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This control, illustrated in the diagram works as follows:
The engine speed is increased by a plunger (1) connected to a spring loaded diaphragm (2) op­erated by engine manifold vacuum (3).
The amount of vacuum which operates the dia­phragm is controlled by a solenoid valve (4) ener­gized when the transmission shift lever is in neutral position. The diaphragm spring (5) is strong enough to overcome the accelerator pedal return spring as well as any friction in the throttle control mecha­nism. When sufficient intake manifold vacuum is applied to port (3) with valve (4) in position shown. the diaphragm and plunger will move into the po­sition shown, until spring (5) is fully compressed. This movement disengages the device from the throttle lever, its normal position in all driving po­sitions other than neutral.
The solenoid (6) is connected in series with the air-conditioning control switch as well as with a switch mounted at -the bottom of the transmission shift lever. This latter switch is closed only when the transmission lever is in neutral position. Hence, when the air conditioning switch is on and the shift lever is moved to the neutral position the solenoid becomes energized and pulls the armature and connecting valve (4) in the closed position. With the valve in the closed position it shuts off vacuum applied to the diaphragm and also bleeds atmospheric air to the diaphragm through the bleed hole (7). When this occurs, spring (5) forces the diaphragm and plunger outward causing the adjusting screw (8) to engage the throttle lever and open the throttle valve the desired amount.
CO, WD, 131, 132:1-9-16, 149, 9X, 9FR
Form 1223 IP S. Printed in U. S.A.

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