Opel 1900 1973, Service Manual

Page: 335 / 625

44 1973 OPEL SERVICE MANUAL
CARBURETOR AND THROTTLE LINKAGE
ALL MODELS
CONTENTS
Subject
DESCRIPTION AND OPERATION:
Carburetor . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DIAGNOSIS:
Carburetor
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MAINTENANCE AND ADJUSTMENTS:
Idle Speed and Mixture Adjustments . . . . . . . . . . . . . . . . . . . . . . . .
Fast Idle Speed Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Throttle Linkage Adjustment . . . . . . . . . . . . . . . , . , . . . . . . . . . . . . . . . . . . . . . .
MAJOR REPAIR:
Remove and Install Carburetor
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Throttle Linkage Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Overhaul Carburetor
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SPECIFICATIONS:
Carburetor Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page No.
DESCRIPTION AND OPERATION
CARBURETOR
The two-barrel carburetor for all 1973 Opel1
Manta and GT models is a down-draft carburetor
with two barrels of 1.25 inch diameter each. It has
an automatic choke and a secondary valve operated
by a vacuum diaphragm, except when installed in an
Opel GT. In the GT, the secondary throttle valve is
operated by mechanical linkage from the primary
throttle valve.
The two-barrel carburetor consists of three main
parts throttle body, float chamber and air horn.
Each barrel is a separate system, but both barrels
discharge into a common inlet in the intake mani-
fold. The secondary barrel does not
a choke
valve or an accelerator pump. See Figure
throttle valve of the primary barrel is opened
through the throttle linkage. When the primary
throttle valve is almost open, at approximately half
of the maximum engine RPM, the secondary throttle
valve is opened
by
vacuum applied through a
vacuum diaphragm case. See Figure The sec-
ondary throttle valve on the GT model is opened by
mechanical linkage from the primary throttle shaft.
Choke System
The automatic choke is operated by a bi-metal
spring. The tension of the spring depending on
temperature of the heater coil decreases with rising
temperature and the choke valve opens progressively
until it is completely opened at engine operating tem-
perature. The choke valve is off-set so that choke
valve opening increases as air flow increases.
If the choke valve is closed, the throttle valve is
opened slightly to provide a fast idle speed. This is
done through a cam, abutment lever and throttle
connecting link. With the throttle valve opened
slightly, the vacuum during cranking can take effect
up to the choke valve, thereby drawing ample fuel
out of the main nozzle. See Figure
With rising temperature of the heater coil, the choke