Bulletin 9D-6
August, 1951
Model "B"
Page 3
ROCHESTER PRODUCTS DIVISION, GENERAL MOTORS CORP.,
ROCHESTER, NEW YORK
THE ROCHESTER GM CARBURETOR
FOR CHEVROLET
The new Rochester Products' Model
"B" Carburetor as used on the Chevrolet engines, presents a number of
distinct new features, features which show themselves in performance for
the car owner and ease of service for the mechanic.
Foremost of the features
contributing to the improved performance is the unique design of the
carburetor float bowl. The new carburetor has a concentric float bowl as
contrasted to an eccentric or one-sided bowl on other type units. This
float bowl concentricity in conjunction with the centrally located main
discharge nozzle prevents any fuel from spilling from the nozzle on road
inclines. Regardless of any angle the car may assume, the fuel level is at
all times below the nozzle spill point.
A second feature of the new Model
"B" Carburetor is the design of the Main Well support Assembly. This
design eliminates any need for an anti-percolator. This assembly contains
the Main Metering Jet and Power Valve. It is attached to the Cover and is
suspended in the fuel of the Float Bowl.
When the engine is not operating,
the rise in heat from the engine manifold is applied to the Float Bowl,
causing fuel percolation or boiling. When the main metering jet is
attached directly to the Float Bowl, it allows the heat to percolate the
fuel in the main passageways. As a consequence, the boiling fuel
seeks escape through the main nozzle and into the engine. This often times
causes difficult hot starting.
However, in the Model "B"
Carburetor, the heat applied to the Float Bowl may cause minor vapors atop
the fuel level but the entry to the main passageways through the main
metering jet is actually insulated and surrounded by the cooler solid fuel
near the bottom of the Float Bowl. This prevents any fuel percolation in
the passageways.
PERFORMANCE FEATURES
For smoother performance at low
speeds the new carburetor has been designed to permit a continuous fuel
flow to the engine. In conventional type carburetors, there is a distinct
transfer point when the direction of fuel flow changes from the idle to
the main metering system. This causes a momentary lag in fuel delivery to
the engine. The Model "B" carburetor by the design of a common passage for
both the idle and main metering systems, enjoys the smoother performance
due to this continuous fuel flow from the idle to the main metering
system.
During the period of engine
warm-up, it is often advantageous to operate the engine with the power
mixtures, without advancing the accelerator to the full wide-open
position. By the use of a vacuum operated power system in the new
carburetor, these power mixtures are readily available. This is due to the
ability of the power valve to function at any drop in manifold vacuum
below 5" Hg., regardless of the degree of throttle opening. In carburetors
which employ a mechanical operated power system, the throttle must be
advanced to the full wide open position to obtain the power
mixtures.
To prevent poor initial
acceleration and to minimize hard starting in hot weather the model "B"
unit employs an anti-percolator type of pump plunger. When the engine is
not operating, the rise in heat from the engine manifold causes the fuel
in the pump system to percolate.
