SUPPLEMENT
The
needle size is engraved on the shoulder
of the needle,
which should be
fitted with the
shoulder
flush with the under
face
of the piston and
retained by tightening the screw.
Jet Centralising
The
jet
unit,
clamped in
position
by a nut,
is held in a
clearance bore
that permits a limited amount of
radial float
Drior
to
being locked.
'
when the"suction
piston is lifted by hand
(air
cleaner
removed
and engine
still), it should fall freely and
hit the
jet
bridge with
a soft
metallic click
that is, with the
jet
adjusting
nut
(5)
Fig. 2,
in its toirmost position. If this test is inaudible,
but
audible
when repeated with thejet
in
the
fully lowercd
Position,
re-centralise the
jet
as
follows:
1. Disconnect
the rod between the
jet
lever and
jet
head.
2. Unscrew
the urion holding the nylon
feed tube into the
base of the float chamber and
withdraw the tube and the
jet
together. Unscrew
the
jet
adjusting
nut and remove
the
lock
spring.
Replace the adjusting nut and screw
it to its
topmost position,
then replace the
jet
and feed tube.
3. Slacken
otr the large
jet
locking screw until the
jet
bearing
is
just
free to rotate by
llnger
pressure.
4,
With the piston damper removed, and using
a
pencil
on
top of the piston
rod,
gently press
the
piston
assembly down
onto the
jet
bridge.
5. Tighten the
jet
locking
screw, observing
that the
jet
head is
still
in its
corrcct angr-rlar
position.
6.
Lift the piston and
check
that it falls freely and evenly,
hitting the
jet
bridge
with
a soft,
metallic click; then fully
lower the
jet
and re-check
the sound of the
imPact; il the
second test produces
a sharper
impact sollnd, repeat tbe
operation
until corect.
7. Refill the damper
reservoir.
Tuning
Carburettors
Twin carburettor
installations cannot
be
successfully
tuned
unless the general
condition of the engine,
ignition and
the
fuel
system is satisfactory.
Remove the
air cleaners and run
the engine untii
it reaches
normal operating
temperature.
Slacken the clamping
boiis
(7)
on
the throttle spindle connections
(Fig.
2). Close the throttles
fully by unscrewing
the idling adjustment
screws
(8)
and
then
open by screwing
down the screws
one and a
half
turns.
R€move the suction
chambers and
pistons. Screw
the
jet
adjusring
nuts
f5)
unlil each
jet
is flu:h
*ith the bridge of its
carburettor.
or as near
lo rhis as
possible. Replace the
Pis(ors
and suction
chamber
assemblies and check
that the pistons fal]
freely. Screw
down the
jet
adjusting
nuts two comPlete
turns.
Re-start the engine
and adjust
the throttle adjusting
screws
by
an equal amount
to give the
desircd
idling
speed
Using a
length of
0 3"
(7
5 mm.) approx.
bore tubing,
listen to the hiss in
the
intakes and adjust
the throttle adjusting
screws until
the
intensitv of the
hiss is similar
at botb
intakes. This will
synchronize
the throttles.
Adjust the mixture
by screwing both
jet
adjusting nuts up
or
down
by the same
amount to give
the fastest
idling sPeed con-
sistent
with even firing.
Press the
jets
upwards
during adjust
ment
to ensure continual
contact
with the adjusting
nuts
(5)
(Fig.
2).
Should
the engine speed
increase as
thejets are adjusted.
ot
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