Sunbeam ALPINE I SERIES: APLINE II SERIES, Workshop Manual

Page: 103 / 413

Section C (Fuel System)
SUNBEAM
Page 17
At about three-quarters throttle opening the engine
suction In the inlet manifold becomes insufficient
to hold the diaphragm and its plunger up against
its return spring pressure. The spring then pushes
the diaphragm and plunger downwards, overcoming
the pressure of the weaker by-pass valve spring and
forcing the by-pass valve off its seat. This allows
extra fuel to pass through the by-pass jet and into
the main discharge jet to supplement the supply
given by the metering jet. The rating (strength) of
the diaphragm return spring is very carefully chosen
and_ the spring must not be altered in any way.
DIAPHRAGM
RETURN SPRING
DIAPHRAGM
PLUNGER
ACCELERATOR PUMP
OPERATING PLUNGER
The accelerator pump (See Figs. 12 and 13)
To ensure immediate acceleration when the throttle
Is suddenly opened, a controlled and metered supply
of fuel is required. This is provided by the acceler­
ator pump, the object of which is to overcome any
tendency for a lag in acceleration when the arc­
burettor is adjusted to give a low consumption at
normal road speeds. It is directly connected to the
throttle spindle by suitable linkage, so that every
time the throttle is snapped open a small quantity
of metered fuel is injected into the air stream.
When the pump piston is at the top of Its stroke,
- FUEL
ACCELERATO, '.
PUMP OPERATING
LEVER
Fig. 12.
By-pass valve and accelerator pump operating mechanism