ENGINE DIVISION SERVICE MANUAL
The outward appearance of 4150 series carburetors
described in this service manual differ with engine model,
vehicle model or year. Manually and automatic operated
chokes are used on the model 4150 and 4150C respectively.
The centrifugal-vacuum type governor is used on the model
4150G and the electronic vacuum modulating governor is used
on the model 4150EG carburetor.
The model 4150 series carburetor is of the four-barrel,
two stage, downdraft type. The first stage (primary stage)
supplies a fuel/air mixture throughout the entire range of engine
operation and contains the choke valve. The secondary stage
constantly supplements the fuel delivery as needed. The
secondary throttle plates are vacuum controlled and operated
by the primary stage and governor.
There are three major subassemblies of the carburetor
and they are: 1) the main body assembly, 2) the fuel bowls and
metering assemblies, and 3) the throttle body assembly.
The die-cast fuel bowls and metering bodies contain the
fuel chambers, fuel inlet needle valves, accelerating pump,
primary and secondary main jets and fuel metering passages.
The die-cast throttle body assembly contains the primary and
secondary throttle plates, throttle linkage and various fuel and
A diaphragm-type operated accelerator pump is located
in the bottom of the fuel bowl. The pump functions when pump
lever is activated by cam on throttle lever assembly. An
override spring on pump lever adjusting screw allows a
prolonged discharge of fuel for smooth acceleration
The primary side of the carburetor utilizes four basic fuel
metering systems. The Idle System provides, supplemented by
the secondary side, a mixture for idle and low speed
performance. The Accelerator System provides additional fuel
during acceleration; the Main Metering System provides an
economical mixture for normal cruising conditions; and the
Power Enrichment System provides a richer mixture when high
power output is required.
In addition to these four basic systems, there is a fuel
inlet system that constantly supplies fuel to the basic metering
systems and a choke system which temporarily enriches the
mixture to aid in starting and running a cold engine.
The secondary side of the carburetor utilizes, depending
on engine model, two or three basic fuel metering systems. The
Idle System supplements the primary side to provide a rich
mixture for smooth idle and low speed performance; the Main
Metering System provides, with the primary system, an
economical cruising mixture; and the Power Enrichment System
(not used on all carburetors) provides a richer mixture when
In addition to the basic secondary systems, there is also
a fuel inlet system to supply fuel to the metering systems.
Fuel Inlet System
Fuel enters the fuel bowls through a filter screen in the
fuel inlet and into the fuel inlet valves which are frequently
referred to as the fuel inlet needle and seat assembly (Fig. 6).
The amount of fuel entering the fuel bowls is determined by the
space between the top of the movable needle and its seat and
also by the pressure from the fuel pump. Movement of the
needle in relation to the seat is controlled by the float and lever
assembly which raises and falls with the fuel level. As the fuel
level drops, the float drops, opening the needle valve to allow
fuel to enter the float chamber.
When the fuel reaches a specified level, the float moves
the needle valve to a position into the seat where it restricts the
flow of fuel, admitting only enough to replace that being used.
Any slight change in the fuel level causes a corresponding
movement of the float, opening or closing the fuel inlet needle
valve to immediately restore or hold the correct fuel level.
The fuel inlet system must constantly maintain 'the
specified level of fuel as all the other metering systems are
calibrated to deliver the proper mixture only when the fuel is at
Prior to the introduction of the emission control systems,
most all fuel bowls were vented to the atmosphere. On later
model carburetors, fuel bowls are vented internally and vapors
are burned in the engine.
CGES-125-T Page 3
PRINTED IN UNITED STATES OF AMERICA