RCB 9D-6

Bulletin 9D-6

August, 1951

Model "B"

Page 5

ROCHESTER PRODUCTS DIVISION, GENERAL MOTORS CORP., ROCHESTER, NEW YORK

IDLE SYSTEM

As shown in Figure 1 the idle fuel first passes from the bowl through the calibrated

Main Metering Jet (A) in the bottom of the Main Well Support Assembly (B). The fuel is then drawn up the Main Well by manifold vacuum (suction) to the crossbar of the Air Horn. Air joins the solid fuel through the three calibrated air bleeds (C) in the center of the crossbar. The fuel/air mixture is then calibrated by the Idle Tube (D) and passes down the passage in the Float Howl to the Throttle Body.

The idle fuel is then metered to the engine by the idle adjusting needle hole (E), which is below the throttle valve (F). As the throttle valve is opened the three idle holes (G) are exposed in turn to manifold vacuum, and deliver additional fuel to meet the increased engine demand.

Figure 1

PART THROTTLE SYSTEM

As the throttle valve (F) is opened to a

greater degree sufficient suction is applied to the main discharge nozzle (II) in the crossbar. As a consequence the fuel begins to pass from the main nozzle, rather than through the idle system.

The calibration of the Main Metering Jet (A) and Air Bleeds (C) in the crossbar control and maintain the economical fuel/air ratios throughout the 25-60 mph driving range.

POWER SYSTEM

To provide additional fuel for sustained high speed operation or increased road load power, the vacuum operated Power System delivers such fuel readily and economically.

A direct manifold vacuum passage (M) within the carburetor to the engine intake manifold operates this system. At any manifold vacuum above 5" Hg. the Power actuating Piston (I) is held by suction in the "Up" position against the compression of the Power Spring (K) consequently no fuel passes through the ball type Power Valve (J). With any decrease in vacuum below 5" Hg. the calibrated Power Spring (K) immediately forces the Power Piston down, which unseats the spring loaded ball (L) in the Power Valve (J). Fuel then passes readily around the ball into the base of the Main Well Support Assembly. The calibrated power restriction (N) meters the fuel prior to joining the fuel from the main metering jet, and is delivered to the engine. Conversely as the manifold vacuum rises above 5" Hg. the Power Piston is drawn immediately to the "Up" position and the engine returns to the economical part throttle mixtures of the Carburetor.

There is no adjustment required for the Part Throttle or Power Systems.