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D
THE FUEL SYSTEM
air
leal<
in
the
pump
or in
its connections,
bubbles
v.ill
be
seen
coming
o ut
of the
pipe
projecting downwards
into the flow-meter. Bubbles
will
certainly come
through
here
for a
short while after starting up, but they should
cease after
the
pump
bas been
running
for a
minute
or
so. The tap should
then be turned
right off
and
tbe
pump should
stand
without
repeating
its
action
for 4t
least 12
seconds.
If it
repeats
within
this time
the suction
valve
is
not
seating correctly.
Fig.
D.4
Cirerking rig
The tap
should
then be
turned on slowly to
see
if
the
pump
idles
satisfactorily and that the
o
uter rocker
comes
forward
till it makes
contact
with the pedestal,
and
while
it
is
in
this
position
the tip
of
the
b lade
should
be
pressed
inwards to reduce the
stroke
of the pump
gradually.
However
much
this
stroke
is
reduced,
the
pump should go
on pumping normaUy
until
it
fails
altogether
owing to there being no gap
left. If
instead
of
pumping it
buzzes,
it usually
indicate.
s excessive
flexibility
in
the diaphragm.
This,
of
course, is
not
likely
to
be experienced
with a
new
diaphragm.
Then, with the
tap
turned on
fully,
the
pump should
be
tested
o
n
10
volts
a nd it
should work satisfactorily
under
these
conditions,
although probably with a
reduced
output.
D.8
It
is
as weU
to
let the pump
run
for
10
minutes
or
so
before carrying out
these
various tests.
The
cover should
then be
fitted and
held
in place
with
two ordinary
brass
nuts fitted on
the
end of the
terminal.
NOTE.-
There are
three
important
points which are
repeatedly
overlooked
by operators. These seriously affect
tbe functioning
of
the
pump;
tbey are:
( I)
To keep the contact breaker
blade
out of contact
while
obtaining
the corred diaphragm
setting.
(2) To press firmly
and stea
dily
on
the armature,
instead
of jerking it
wblle
obtaining the
settiDg.
(3) Omission
to
stretda
the
diaphragm to the limit
of
its stroke
while
tightening
up the
body screws..
Section
D.7
TRA
O
N
G FUEL
PUMP
TROUBLFS
Should
the
pump
cease to
function,
first
disconnect
the fuel
delivery
pipe
from the pu mp.
If
the pump then
works the
most
likely
cause of
the
t rouble is
a
sticking
needle
in
the
float-chamber of the carburetter. Should
the pump
not work, disconnect the lead
from
the
terminal
and
strike
it against
the
body of
the
pump after
switching
on
the
ignition.
If
a spark oocurs
it
indicates
that the
necessary
current is
available at
the
terminals and
that
the
trouble arises
wi th the
pump mechanism.
lf
no
spark
can
be detected, then it is an indication that the
current
supply has failed and that attention
should be given
to
the wiring
and
battery. If no current is present,
further
investigation should be carried out
by removing the
bakelite
cover which is
reta
ined by the terminal out.
Touch
the
terminal
with
the
lead. If the
pump
does not
operate
and
the
contact
points are in
contact, yet
no
spark
can
be struck off the terminal,
it
is very
probable
t hat
the contact
points are
dirty and require cleaning.
These may be cleaned by
inserting
a
piece of
card between
them,
pinching them together,
and
slid
ing
the
card back-
wards a nd forwards.
It
is
possible
that there
may
be
an
obstruction
in the
suction
pipe,
which
should
be cleared by blowing
air
through
it,
or
tbat
some irregularity
in
the
pump
itself
is preventing the correct movement.
This
may be d ue
either
to
the
diaphragm having
stiffened, or to foreign
matter
in
the roller assembly which supports
the dia-
phragm,
in
which case the diaphragm should
be
removed
and the whole
assembly
cleaned
and reassembled in
accordance with the instructions
given
in Section
0 .5.
On
the
other hand,
if
the points are
not making
contact
see
that
the
tips of the
inner
rocker
( 12) are in
contact
with
tbe
magnet
housing.
If
they are not, it is
an
indication
that
the
armature
has
failed
to
return
to
the end
of
its no rmal travel.
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