
128 LIGHT AND HEAVY VEHICLE TECHNOLOGY
kFuel level
Main jet
Large throttle \
Economiser jet
opening
J
■IECO
no
miser
4
^ jet
opened
Throttle connection
(a)
Large throttle released
opening
\ \ I [Sjjjlj^cono miser jet
opened
Intake manifold connection
(b)
Figure 6.15 Action of fixed-choke carburettor power/
economizer fuel jet
systems:
(a) mechanically operated
(b) pneumatically operated
pneumatically operated economy air valve may be em-
ployed, which is normally retained open against a
spring-loaded diaphragm, the chamber for which com-
municates with the engine side of the throttle valve
(Figure 6.16). In operation, the air valve closes onl