to a the lower end of a piston controlled by the suction from the engine.
As
this suction increases the needle is gradually withdrawn from the jet, enlarging
its effective opening and
permitting it to pass more petrol.
The jet is so mounted that
it
may
readily be moved up or down relative
to the tapered needle, in order to weaken or strengthen the mixture over the
whole working range, by
a
lever operated from the mixture control lever on
the near side of the dash. This control provides an enriched mixturle to
ensure easy starting and even running when the engine is cold. The mini-
mum jet opening can accurately be set by means of the adjusting nut, which
forms an abutment for the enlarged head of the jet.
The carhuretter is extremely simple, and its adjustment is equally simple
if
it
is remembered that the jet is of
a
fixed stondnrd size and cannot be altered.
r..
I
he only possihle adjustmment, other than the slow-running adjustment, is
the fitting of a new needle of a different size. Since a needle of the correct
size is fitted at the Works before the car is dispatched, this adjustment should
not be required, and the suction chamber is therefor,e sealed.
ADJUSTING.
Run the engine until it attains its normal running temperature.
Screw the jet adjusting nut upwards as far as it will go and disconnect
the mixture control rod from the end of the brass lever actuating the jet.
Push this jet actuating lever towards the body of the carburetter as far
as it will go, then slowly move it away from the carburetter (thus
gradually weakening the mixture) until the engine idles evenly, Bring
on all four cylinders regularly.
The jet adjusting nut should now be unscrewed until its head just
comes into contact with the jet head. This will be the normal slow=
running position when the engine is hot, and as the jet needle is of the
correct size the general performance of the carburetter on the road
should be entirely satisfactory.
The mixture control rod may now be reconnected to the jet
actuating lever.
The correct position for the tapered needle is with its shoulder flush
with the face of the piston.
Sources of Troubl~e.
There are only three trouhles which may aff'ect the
functioning of the
S.U.
carburetter.
1.
The piston may be sticking and not functioning properly.
2.
There may be dirt or water in the carhuretter.
3.
The float mechanism
m:ly
have become deranged, and the carburetter
is in consequence flooding.
Piston Sticking.
The suction piston consists of the piston proper forming
the choke; the suction disc, into which is inserted the hardened and ground
piston rod working
in
a
be:~ring in the suction chaniber; and a tapered needle
regulating the jet opening.
If
the piston is sticking this can easily be ascer-
tained by inserting
a
finger in the air intake and raising the piston. The
piston should come up quite freely and return to its seat with
a
click as soon
as
it
is released.
D/I
PAGE
FIFTY-SEVEN
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