FUEL
SYSTEM
interior of the spindle contains a quantity
of thin engine oil, and the marked retarding
effect upon the movement of the main
piston assembly, occasioned by the resist-
ance of the small piston, provides the
momentary enrichment desirable when the
throttle is abruptly opened. The damper
piston is constructed to provide a one-way
valve action which gives little resistance to
the passage of the oil during the downward
movement of
the
main piston.
An
ignition connection (27 in Fig.
8
or 33
in
Fig.
9)
is provided for use in con-
juction with suction-operated ignition
advance mechanism, and is fitted to the
front carburettor only.
THROTTLE
AND
MIXTURE
CONTROL INTERCONNECTION
Fig.
9
A
direct connection is provided between the
jet movement and the throttle opening.
Such an
interconnection ensures that the
engine
will
continue to
run
when the
mixture is enriched by lowering the jet,
without the additional necessity of main-
taining a greater throttle opening than is
normally provided by the setting of the
slow-running screw (2).
Fig.
p
Throttle and
Mixture
Control intercon-
nection.
The mechanism involved in
this
inrer-
connection is shown in Fig.
9.
It will be
seen thar a connecting rod (32) conveys
movement from the jet lever (23) to a
level
(31) pivoted on the side of the main body
casting.
Movement of the jet lever in the direction
of enrichment is thus accompanied by an
upward movement of the extremity of the
lever (31) which, in turn, abuts against the
adjustable screw
(30)
and this opens the
throttle to a greater degree than the normal
slow-running setting controlled by the
slow-running stop screw (2). The screw
(30) should be so adjusted that it is just
out of contact with the lever (31) when the
jet has been raised to its normal running
position, and the throttle is shut back to
its normal idling condition, as determined
by the screw
(2).
38.
EFFECT OF ALTITUDE
AND
CLIMATIC EXTREMES ON
STANDARD
TUNING
The standard tuning employs a jet needle
which is broadly suitable for temperate
climates at sea level upwards to approxi-
mately
3,000
ft.
Above this altitude it
may be necessary, depending on the addi-
tional factors of exteme climatic heat and
humidity, to use a weaker tuning thar
standard.
The factors of altitude, extreme climatic
heat, each tend to demand a weake:
tuning, and a combination of any of
thesl
factors would naturally emphasise
thi
demand. This is a situation which canno
be met by a hard and fast factory recom
mendation owing to the wide variations
L
the condition existing and in such case
the owner will need to experiment wit
alternative weaker needles until one
i
found to be satisfactory.
If the carburettor is fitted with a spring
loaded suction piston, the necessary weaker
ing may be affected by changing to a weakc
type of spring or by its removal.
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