Adjustment
As the needle size is determined during engine development, adjustment
of the carburettors is confined to correct idling adjustment. Remove the
air cleaners and
run
the engine
until
it has attained its normal running
temperature slacken one of the clamping bolts
(B)
on the throttle spindle
connection and disconnect the mixture control link
(G)
by removing one
of the fork swivel pins. Adjust the idling speed to approximately
500
r.p.m. by moving each throttle adjusting screw
(A)
&
(C)
an equal
amount. By listening to the hiss in the intakes, adjust the throttle adjusting
screws
until
the intensity of the hiss is similar on both intakes. This
will
synchronise the throttles. When this is satisfactory, the mixture should
be adjusted by screwing both the jet adjusting nuts
(E)
up or down to
exactly the same extent, at the same time keeping the jet levers
(F)
pressed forward to ensure that the jets are hard up against the nuts, until
even running is obtained. As these are adjusted, the engine will probably
m
faster, and it may therefore be necessary to unscrew the throttle
adjusting screws a little, each by the same amount,
in
order to reduce the
speed. When the mixture is correct on both carburettors, lifting the piston
of one of them with a penknife blade should make the engine beat become
irregular from excessive weakness. If lifting the piston about
3"
(3
mm.)
on one carburettor stops the engine and lifting the other about
Q'"
increases the engine speed, this indicates that the mixture on the
first
carburettor is set weak and the second is set rich. The first one should,
therefore, be enriched by unscrewing the jet adjusting nut one flat at
a
time and the second should be weakened off by screwing up the jet
adjusting nut in a similar manner. When the mixture is correct, the
exhaust beat should be regular and even.
If it is irregular, with the splashy type of misfire and a colourless exhaust,
the mixture is too weak. If there is a regular or
rythmical type of misfire in
the exhaust
beat, together with a blackish exhaust, then the mixture is too
rich. This should be noted when the air cleaners are again in position.
When reconnecting the mixture control link, make sure that the jet levers
are pressed
forward and the control rod
adjusted correctly for length so
that the clevis pins may be inserted freely while the jets are in this position.
The throttle spindle interconnection clamping bolts
(B)
should now be
tightened.
The desired fast idle necessary when the choke is in operation is con-
trolled by adjusting screw
(D).
For further information on the tuning, adjustment and maintenance of
S.U. carburettors, you are advised to get in touch with the S.U.
Car-
burettor Co. Ltd., Wood Lane, Erdingron, Birmingham
24,
from whom
the necessary literature may be obtained.
Fuel
Pump
The mechanically operated fuel pump, mounted on the left-hand side of
the crankcase, provides a constant pressure of fuel
to
the carburettor.
A
hand primer is fitted, which can be used to pump fuel to the carburettors
29
SPORTS
CAR
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