Opel 1900 1973, Service Manual, Page: 339 / 625

1973 OPEL SERVICE MANUAL
ary barrel, it is provided with transfer system.
When the secondary throttle valve starts to open,
two‘ports (which are normally just above the closed
valve) are uncovered, causing fuel to feed into the
secondary bore just before the secondary
nozzle
starts feeding. This provides for an additional enrich-
ment of the air-fuel mixture at the beginning of full
throttle operation. See Figure
n
Figure Primary to Secondary Transfer System
Enrichment System
If the secondary throttle valve is fully opened, the
vacuum in the throttle valve area is reduced so that
the transfer ports (mentioned above) stop feeding.
However, the vacuum increases greatly in the sec-
ondary venturi area. An enrichment tube which pro-
trudes into the primary venturi area, feeds fuel
continuously during full throttle operation. See Fig-
ure
Acceleration System
Whenever the throttle is closing, the suction stroke
of the diaphragm pump causes fuel to flow from the
float chamber through the inlet ball valve into the
pump chamber. When the throttle valve is opened
the diaphragm is moved inward by the pump con-
necting rod
and the pump lever. Fuel is injected into
the primary bore through the injector tube. The
amount of fuel is determined by the pump stroke.
The inlet ball valve in the pump chamber prevents
fuel from flowing back into the float chamber during
the pressure stroke of the pump. The outlet ball valve
prevents air from being drawn into the injector tube
during the suction stroke of the pump. See Figure
8.
Float Bowl Ventilation
While driving, the float bowl is ventilated from inside
Figure Acceleration System
the carburetor. That is, the float bowl is connected
through the vent valve with the area under the air
cleaner.
When the engine is idling or off, the ventilation from
inside is cut off and ventilation from the charcoal
canister is cut in. The upper spring now seats the
valve on the upper seat. See Figure
Figure Float
Ventilation
The advantage of an inside vent while driving is that
air cleaner restriction does not
the air fuel
mixture. The purpose of the charcoal canister vent
while idling or after shutting-off a hot engine, is to
prevent
excess fuel vapors from entering the intake
manifold and outside air. Excess fuel vapors may
cause an idling engine to stall, or may make it dif-
ficult to restart a hot engine.