Opel 1900 1973, Service Manual

Page: 338 / 625

CARBURETOR AND THROTTLE LINKAGE
4 7
Figure Secondary Vacuum Diaphragm
Figure Automatic Choke System
Figure System
in a richer mixture. When the throttle valve is
opened, fuel is also drawn from the upper ports,
providing a good transfer from the idle system to the
main metering jet system. See Figure
Main Metering Jet System
During high-speed operation, fuel is drawn from the
float chamber through the main metering jet (Figure
into the emulsion tube bore. The emulsion
tube, which is provided with transverse bores, is in-
serted in the emulsion tube bore. Vacuum in the
primary venturi (Figure
draws fuel from the
main nozzle. As the vacuum increases, the tendency
is to draw too much fuel from the main nozzle, mak-
ing the mixture too rich. To compensate for this
tendency, the fuel level drops in the emulsion tube
bore and more emulsion tube transverse bores are
exposed. Air from the high speed air jet (Figure
enters the emulsion tube through these trans-
verse bores and mixes with the fuel. The more the
fuel level drops, the more the transfer bores are ex-
posed. This causes the air-fuel ratio to remain con-
stant over the whole engine speed range. See Figure
Figure High Speed System
The secondary valve diaphragm is operated by
vacuum taken from the mixing chamber of the pri-
mary barrel on the Opel 1900 and Manta only. With
the primary throttle valve almost open and with en-
gine speed at approximately half of the maximum
engine RPM, vacuum increases to such an extent
that the secondary throttle valve starts opening from
vacuum applied in the vacuum diaphragm case act-
ing through a connecting rod and throttle valve
lever. See Figure
Primary to Secondary Transfer System
In order to have a smooth engagement of the