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5.
With a downwards pressure on the throttle adjusting screw (3), adjust
the appropriate screw until the level of hiss is similar at both carburettor
intakes and the idling speed approximately 500 r.p.m.
To reduce hiss at carburettor intake, UNSCREW the adjusting screw.
6.
When level of hiss is similar, stop engine and with a downward pressure
on the rear throttle arm, tighten the throttle spindle clamping bolt and
re-check hiss.
7.
Start the engine and allow it to idle at approximately 500 r.p.m.
Check mixture on each carburettor in turn by lifting the piston approxi-
8.
"
mately ⅛
9.
If when the piston is lifted the engine speed increases the mixture is too
rich and the nut (7) should be screwed up one flat. If the engine speed
decreases unscrew nut (7) one flat.
10.
Continue adjustment on each carburettor until when the piston is lifted,
no increase, or a very slight increase followed by a fall in engine speed is
noticed. The mixture is then satisfactory and the exhaust note should be
regular and even.
11.
Attach choke cable (if previously disconnected). Reconnect the mixture
control rod, ensuring that the jet levers are pressed forward and the
control rod is adjusted correctly for length.
12.
Replace air cleaners.
13.
Re-check idling speed and mixture.
Jet Centralizing (Fig. 28)
When the suction piston is lifted by hand (engine not running), it should fall
freely and hit the jet bridge with a soft metallic click—that is, with the jet
adjusting nut (7) in its topmost position.
If this click is not audible, but is so when the test is repeated with the jet in
the fully lowered position, then the jet unit requires re-centralising on the
needle, as described below.
It may be helpful to understand that the complete jet unit, clamped in
position by the gland nut (4), is held in a clearance bore that permits a limited
amount of radial float, prior to being locked. Therefore, if the gland nut is
slackened, the jet assembly can be moved until it is concentric with the needle,
thus enabling the piston to move freely to its lower position.
The procedure for re-centralising is as follows :
1.
Remove air cleaners.
2.
Remove return spring (6), pivot pins (8), and swing linkage to one side
(disconnect the choke cable if necessary).
3.
Withdraw jet (9), unscrew adjusting nut (7) and remove spring (5).
4.
Remove damper assembly (2).
Replace adjusting nut (7), screwing it to its upper position.
5.
6.
Slacken gland nut (4) and insert jet (9).
RUNNING ADJUSTMENTS
(3 mm.) with a pen-knife blade or lifting pin (3) (Fig. 28).
34
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