FUEL
SYSTEM
(ii)
The piston is meant to be a
fine clearance
fit
at its outer
diameter in the suction chamber
and a sliding
fit
in the central
bush. The suction chamber
should be removed, complete
with piston, and the freedom of
movement checked after removal
of the damper rod. The assembly
should be washed clean and very
lightly oiled where this slides in
the bush and then checked for any
tendency of binding. It is per-
missible to carefully remove,
with a hand scraper, any high
spots on the outer wall of the
suction chamber, but no attempt
should be made to increase the
clearance by increasing the general
bore of
the
suction chamber or
decreasing the diameter of the
piston. The fit of the piston in
its central bush should be checked
under both rotational and sliding
movement.
(b) Eccentricity of Jet and Needle
Fig. 8.
The jet (14) is a loose fit in its recess
and must always be centred by the
needle before locking up the clamping
ring (15).
(i) The needle should be checked in
the piston to see that it is not bent.
It will be realised that it does not
matter
if
it is eccentric as the
adjustment of the jet allows for
this, but a bent needle can never
have the correct adjustment. For
"
Centralisation of Jet
",
see page
.
,,
IY.
(c) Flooding from Float Chamber or
Mouth
of
Jet.
Fig.
8a.
This
can
be caused by a punctured
float (10) or dirt on the needle valve
(9)
or its seat. These latter items can
be readily cleaned after removal of the
float chamber lid.
(d)
Leakage
from Bottom of Jet
adjacent to Adjustment Nut.
Leakage in this vicinity is most likely
due to defective sealing by the upper
and lower sealing gland assemblies
There is no remedy other than
removing the whole jet assembly after
disconnecting the operating lever and
cleaning or replacing the faulty pans.
It is very important that all parts are
replaced in their correct sequence, as
shown in the illustration, and it must
be realised that centralisation of the
jet and needle and re-tuning will be
necessary after this operation.
(e) Dirt in the Carburettor
This should be checked
in
the normal
way by examining and cleaning the
float chamber, but it may be necessary
if excessive water or dirt is present to
strip down and clean
all parts of the
carburettor with petrol.
(f) Failure of Fuel Supply to Float
Chamber
If the engine is found to stop under
idling or light
running
conditions,
notwithstanding the fact that a good
supply of fuel is present at the float
chamber inlet union (observable by
momentarily disconnecting this), it is
possible that the needle has become
stuck to
it3 seating. This possibility
arises
in
the rare cases where some
gummy substance is present in the fuel
system. The most probable instance
of this nature is the polymerised
gum
which sometimes results from the
protracted storage of fuel in the tank.
After removal of the float chamber
lid and float lever, the needle may be
withdrawn, and its point thoroughly
cleaned by immersion in alcohol.
Similar treatment should also be ap-
plied to the needle seating, which
can conviently be cleaned by means
of a matchstick dipped in alcohol.
Persistent trouble of this nature can
only be cured properly by complete
mechanical cleansing of the tank and
fuel system. If the engine is found
to suffer from a serious lack of power
which becomes evident at higher speeds
and loads, this is probably due to an
inadequately sustained
he1 supply, and
the fuel pump should be investigated
for inadequate delivery, and any filters
in the system inspected and cleansed.
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