RCB 9D-6

Bulletin 9D-6 August, 1951 Model "B" Page 6 ROCHESTER PRODUCTS DIVISION, GENERAL MOTORS CORP. ROCHESTER, NEW YORK

FLOAT SYSTEM The Model "B" Carburetor is completely balanced. The balance tube connects the carburetor air intake and the float bowl, thereby equalizing air pressures. In this manner any accumulation of dirt in the air cleaner is compensated for and prevents any erratic mixtures. To aid in maintaining the correct fuel level under all conditions the carburetor employs twin floats. It is of the utmost importance that the floats be adjusted carefully and accurately. See adjustments bulletin for correct float setting.

PUMP SYSTEM To provide fuel for smooth quick acceleration a double spring pump plunger is used in the Model "B" Carburetor. The rates of compression of the top spring versus the bottom spring is calibrated to insure a smooth, sustained charge of fuel for acceleration. As shown on Figure 2, to exclude dirt all fuel for the pump system first passes through the pump screen (4) in the bottom of the float bowl. It is then drawn past the ball check (5) into the pump well on the intake stroke of the plunger. Upon acceleration the force of the pump plunger seats the ball check (5) and forces fuel up the passage (6). The pressure of the fuel lifts the pump outlet ball check and spring (7) from its seat. The fuel is then sprayed on the bottom edge of the Venturi by the pump jet (8) and delivered to the engine.

No targeting of the Pump Jet is required.	Figure 2

For greater driving ease the pump plunger head has been designed to eliminate fuel percolation in the pump system. This has been accomplished by the unique design of a ball check and seat (1) in the plunger head (2). When the engine is not operating any build up of fuel vapors in the pump well rise and by-pass the ball. This allows the hot fuel and vapors to circulate up the passage (3) in the plunger head and return to the float bowl. Without this feature, any vapor pressure built-up would evacuate the fuel in the pump system into the engine manifold, causing poor initial acceleration due to lack of fuel in the pump system.