Opel 1900 1973, Service Manual, Page: 353 / 625

62 1973 OPEL SERVICE MANUAL
bleed into the line, allowing more manifold
vacuum to reach the vacuum motor. Whenever there
is nine inches or more of vacuum in the vacuum
motor, the diaphragm spring is compressed, the door
is opened.
When the engine is not running, the diaphragm
spring will always hold the door closed. However,
when the engine is running, the position of the door
depends on the air temperature in the air cleaner.
When starting a cold engine (air cleaner temperature
under 85 degrees), the air door will open immedi-
ately. This is because the air bleed valve in the sensor
is closed so that full manifold vacuum, is applied in
the vacuum motor. As soon as the air cleaner starts
receiving hot air from the heat stove, the sensor will
cause the air door to close partially, mixing cold air
with the hot air as necessary to regulate air cleaner
temperature within 20 degrees of the ideal 115 de-
grees air inlet temperature.
If underhood air temperature rises to 135 degrees,
the air bleed valve in the sensor will be wide open so
that vacuum to the vacuum motor approaches zero.
The diaphragm spring in the vacuum motor will hold
the air door closed tightly. If underhood temperature
rises above 135 degrees, carburetor inlet air tempera-
ture will also rise above 135 degrees.
While air cleaner temperature is being regulated, ac-
celerating the engine hard will cause the vacuum
level in the intake manifold and in the vacuum motor
to drop. Whenever vacuum drops below 5 inches, the
diaphragm spring will close the air
door
in order to
get the outside air flow required for max-
imum acceleration.
The carburetor is set by the manufacturer for
850 RPM (automatic transmission) or 850-900 RPM
(manual transmission) and 1.5 to 2.5 percent CO.
Figure E.G.R. System
EXHAUST GAS RECIRCULATION SYSTEM
All 1973 Opel Manta’s and a r e
equipped with an exhaust gas recirculation (E.G.R.)
system. See Figure
The E.G.R. system consists of a pipe connected to
the center of the front exhaust pipe, an E.G.R. valve,
a short pipe from the valve to the intake manifold
and a short vacuum hose from the E.G.R. valve to
the base of the carburetor. See Figure
The system does not receive sufficient vacuum at idle
to operate, but will operate during acceleration and
part throttle providing sufficient intake manifold
vacuum is present.
Figure E.G.R. Valve Location
DIAGNOSIS
TESTING THERMO AIR CLEANER OPERATION
Since failure of the air cleaner will generally
result in the snorkel air door staying open, failure
will probably go unnoticed in warm or hot weather.
In cold weather, however, owners will complain of
hesitation, sag, surge, or stalling. When any
type of lean operation complaint is received, always
test the thermo air cleaner for
functioning
before doing any work on the carburetor.
Always perform checks in the same order as listed
below.
Vacuum Motor Check
1. Check all hoses for proper hookup. Check for
kinked, plugged, or damaged hoses.