
CARBURATION AND FUEL INJECTION 135
municates with the primary choke system. In operation,
the depression in the primary choke system must reach
a value high enough to overcome the diaphragm spring
loading before the secondary throttle valve is opened,
which then brings into action the secondary choke and
jet system (Figure 6.26).
Compound carburettors that utilize either mechanical
or pneumatic operation for delayed movement of the
secondary throttle valve are also known as progressive
choke carburettors or, in modern terminology, sequen-
tial carburettors.
6.5 PETROL ENGINE FUEL INJECTION
General background
In order to gain a general insigh ...