Sunbeam ALPINE I SERIES: APLINE II SERIES, Workshop Manual

Page: 101 / 413

WSM.124
Section C (Fuel System)
with. Fig. 9 illustrates carburettor action under
idling conditions, and the inset, the progression
holes which operate on fast idling.
Part and full throttle operation (See Fig. 10)
As the throttle is opened beyond the slow running
position, the main carburettor comes into action
and suction at the small venturi draws fuel from the
main discharge jet.
When the fuel level falls in the main discharge jet
a series of holes which are in communication with
the atmosphere through the high speed bleed are
uncovered. The fuel issuing from the main jet is
consequently partly atomised by air entering these
holes and is completely broken up when entering
the small venturi. It then passes through the large
venturi to the induction system.
On the WIP carburettor the discharge characteristic
of the main discharge jet is such that a correct
STRANGLER
(FULLY OPEN)
MAIN METERING THROTTLE VALVE
JET
( PARTLY OPEN)
I
st re-issue
Page 15
mixture is given over the light throttle to full
throttle range.
On the WIA carburettor part throttle operation
is similar to the WIP carburettor, but at wider
throttle openings fuel ·is supplied by a by-pass jet
as well as by the metering jet, as described in the
following paragraphs.
Some carburettors are fitted with an accelerator
pump nozzle with a sloping end as shown in inset
'A' of Fig. 13. This type of nozzle allows fuel to be
drawn from it when the air volocity, past its sloping
end, is high enough to create the depression required
SMALL VENTURI
LARGE VENTURI
�-
.... AIRFLOW
-FUEL
Fig. 10.
Part throttle
(cruising)
operating condition.
Full throttle operating condition shown in inset above