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the throttle adjusting screw and again adjust
the pilot air adjusting screw until the idling is
satisfactory.
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Note: When new or re-assembled carburetors are
used, start with pilot screw 1 1/2 turns out from
the fully-in position.
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3. Throttle Cutaway - Throttle one-eight
to one-quarter open.
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If, as the machine pulls away from the idling
position, there is spitting back from the
carburetors, slightly richen the mixture by
screwing in the pilot air adjusting screw slightly.
If this is not effective, return the screw to its
former position and fit a throttle slide with a
smaller cutaway. If, with the throttle in this
position, the engine ji jerks under load and there
is no spitting, either the jet ~ needle is much too
high or a throttle slide with a larger cutaway is
required to cure richness.
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4. Throttle Needle - Throttle one-quarter
to three quarters open.
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The needle controls a wide range of throttle
opening and therefore the acceleration. Placing the
needle in the lower position, that is, with the
clip in the top groove gives a weaker mixture.
Placing the needle in the higher position, that is,
with the clip in the bottom groove, richens the
mixture. If the mixture is too rich with the needle
in the lower position, the needle jet should be
replaced and if the needle itself has had a great
deal of use replace it also.
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5. Pilot Jet
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Check again pilot adjustment as the last
operation.
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SECTION E8
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ADJUSTMENT FOR ALTITUDE
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It is necessary to adjust carburation on a
motorcycle operated continuously in altitudes
greater than 3,000 feet approximately. Motorcycles
as supplied from the factory are already equipped
for correct carburation up to 3,000 feet.
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The main jet requires a reduction in size of 5
per cent at altitudes between 3,000 and 6,000 feet.
Beyond 6,000 feet further reductions of 4 per cent
should be made.
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Altitude adjustments should only be made if the
motorcycle is used permanently at high altitudes.
It is not necessary to adjust merely for a journey
through mountainous areas.
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SECTION E9
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TWIN CARBURETOR ADJUSTMENT
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It is necessary periodically to synchronise the
carburetors so that they open and close
simultaneously. Start with the handiebars in the
centre position so that there is no "pull" on the
throttle cable which will interfere with
adjustment. Proceed as follows:
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1
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Take up any slack in the throttle cables using
the = adjuster on the top of each mixing chamber,
then tighten the adjuster locknuts.
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2
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Start the engine - this must be thoroughly
wermed up before adjustment commences.
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3
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Follow the main adjustment sequence in Section
E7 before setting slow running. It is all-important
to have both throttle valves opening
simultaneously. To ensure that this is the case,
the twist-grip should be set to allow the engine to
run fractionally over idling speed. Gently screw in
the throttle valves in that position. Return the
twist-grip to the closed position so that the
engine runs on the throttle stops. Now proceed as
follows:
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4
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Lift off one spark plug lead and commence
setting the carburetor on the other cylinder as a
single unit.
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5
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Adjust the pilot air screw and stop screw on the
cylinder which is firing.
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6
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Reverse the process by replacing one plug lead
and removing the other.
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7
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Adjust the pilot air screw and stop screw on the
second cylinder.
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8
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Replace the plug lead - at this stage tickover
may be too fast. If so, lower both throttle stop
screws by an equal amount until idling is correct.
Ensure there is. about 1/4" (6 mm) slack in
throttle cable. This slack must be equalized so
that throttles open together.
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SECTION E10
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AIR FILTER
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The airbox comprises a detachable front plate,
perforated metal band and replaceable automobile
type air filter element, the backplate being
mounted directly on to the front of the battery
tray.
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