THE
FUEL SYSTEM
‘
D
3.
If the
engine
speed
momentarily
increases
very
slightly,
the
mixture
strength
of the
rear
carburetter
is
correct.
Repeat
the
operation
at
the
front carburetter,
and after
adjustment
re-check the“
rear
carburetter,
since
the
V
carburetters
are
interdependent.
When
the
mixture
is
correct
the
exhaust
note
should be
regular
and
even.
If
it is
irregular,
with
a
splashy
type
of
mis■re and
colourless exhaust,
the
mixture is
too
weak.
If
there
is
a
regular
or
rhythmical
type
of mis■re
in
the
exhaust beat,
together with
a
blackish
exhaust,
then
the
mixture
is
too
rich.
The
carburetter
throttle
on
each carburetter
is
operated by
a
lever
and
pin,
with the
pin
working
in
a
forked lever
attached
to
the
throttle spindle. A
clearance
exists
between
the
pin
and the
fork which
must
be maintained when
the
throttle
is
closed
and the
engine
idling,
to
prevent
any
load
from
the accelerator
linkage
being
transferred
to
the
throttle
butter■y and spindle.
To
set
the clearance
on
synchromesh
cars,
with the
throttle
shaft
levers
free
on
the
throttle
shaft, place
a
.12 in.
(.3
mm.)
feeler
gauge
between
the throttle
shaft
stop
and the
choke
interconnecting
rod
(see
Fig.
D.l2).
0n
cars
■tted
with
automatic
transmission
place
a
.020 in
(.5 mm.) feeler
gauge
between
the
throttle
lever
and the
throttle lever
stop
(inset, Fig.
12).
Move
each throttle
shaft
lever
downwards
in
turn
until the lever
pin
rests
lightly
on
the lower
arm
of
the
fork
in
the carburetter
throttle lever.
Tighten the clamp bolt
of the
throttle
shaft
lever
at
this
position.
When both carbu-
retters
have been dealt
with,
remove
the feeler
gauge.
The
pins
on
the throttle
shafts should then
have clearance
in
the forks.
Reconnect
the
choke cable,
ensuring
that
the
jet
heads
return
against
the lower
face
of
the
jet
adjusting
nuts
and
that the choke actuating
levers
are
fully returned when the
choke control
is
pushed fully
in.
Pull
out
the
mixture
control
knob
on
the dash panel until
the linkage
is
about
to
move
the
carburetter
jets
(a
minimum
of
%
in.
or
6
mm.)
and adjust
the
fast-idle
adjusting
screws
to
give
an
engine
speed
of
about
1,000
rpm.
when
hot.
A
small clearance
must
be maintained between
the
fast-idle
cams
and
the abutment
screws
when the
mixture
control
is
pushed
fully
in.
Jet-centring
To
check
the
jet
for
concentricity
with the
jet
needle
set
the jet
head and
the
jet
adjusting
nut
in
the
uppermost
position,
lift the
suction piston
with the
piston
lifting
pin,
and allow
the
piston
to
fall.
It
should
fall freely,
and
a
definite
soft, metallic click
will
be
heard
as
the base
of
the
piston
strikes
the
jet
bridge.
’
It
this does
not
happen
with the jet
raised,
but does
occur
when the' jet
is
lowered,
the
jet
bearing and
jet
must
be
recentred
as
follows.
Disconnect
the lever
between
the
interconnecting
lever and
the
jet
head.
L
Unscrew the
union
holding
the
nylon
feed
tube
into
the
base
of
the
■oat-chamber
and withdraw the tube and jet
together.
MGB. Issue
5.
86842
Unscrew
the
jet
adjusting
nut
and
remove
the lock
spring;
screw up
the
nut to
its
fullest
extent
and re■t the
jet head
and feed tube.
Slacken
off the
jet
locking
nut
until
the
jet bearing is
just
free
to rotate
with ■nger
pressure.
Remove
the
piston
damper
from the
top
of
the
suction
chamber and gently
press
the
piston
down
onto
the
jet
bridge.
Tighten the
jet
locking
nut, at
the
same
time ensuring
that
the
jet
head
is
still
in its
correct
angular
position.
Lift
the
piston
and check that
it
falls
freely
and evenly, hitting
the
jet
bridge with
a
soft,
metallic click, with the
jet in
the
raised and
lowered
position.
If the
result
is
not
satisfactory
and
the
piston
is
not
sticking,
the
recentring operation
must
be repeateduntil the
correct
result
is
obtained.
When theoperation
is
complete replace the adjusting
nut
lock
spring
and the
jet
operating
lever.
The
adjustment
is
best
effected with the
carburetters
removed
from the
engine.
Float-chamber
The
position
of the hinged
■oat lever
must
be
such that the
level
of
the
float (and therefore the height of the
fuel
at
the
jet)
is
correct.
To check the
■oat-level, hold
the
■oat-chamber lid and
■oat assembly upside—down and place
a
A}
in.
(3.18
mm.)
diameter bar
across
the diameter
of
the machined lip
of
the
■oat-chamber lid, parallel
to
the ■oat lever hinge
pin
and
under the
■oat
lever
(see
Fig. DJ
1).
The
face of
the
■oat
lever should
just
rest
on
the bar when
the ■oat needle
is
held
fully
on
its seating.
If this
is
not
so,
carefully
reset
the
angle made between the straight
portion
of
the
■oat lever
and
its
hinge until the
correct
position
is
obtained
Float-chamber
■ooding
This
is
indicated by the fuel dripping
from
the drain
pipe,
and
is
generally
caused by
grit
between
the ■oat-chamber
needle
and
its
guide. This
is
cured
by
removing
the
■oat-chamber, washing
the
valve
and
■oat-chamber
components,
and reassembling.
Float needle
sticking
If the
engine
stops,
apparently through lack of
fuel,
when
there
is
plenty
in
the tank» and the
pump
is
working
,
properly, the probable
cause
is
a
sticking ■oat needle.
An
easy
test
for
this
is
to
disconnect
the
pipe
from the electric
pump
to
the carburetters and
switch the
ignition
on
and
off
quickly while the end
of the
pipe is
directed
onto
a
pad
of
cloth
or
into
a
container.
If
fuel
is
delivered,
starvation
is
almost
certainly
being
caused by the
■oat needle
sticking
to
its seating,
and the
■oat-chamber lid
should
therefore
be
removed
and the
needle
and
seating
cleaned
and
re■tted.
At
the
same
time
it
will be
advisable
to
clean
out
the
entire
fuel feed
system
as
this
trouble
is
caused by
foreign
matter
in
the
fuel,
and
unless this
is
removed
it is
likely
to
recur.
It
is
of
no use
whatever renewing
any
of the
component
parts
of
either
carburetter,
and the only
cure
is
to
make
sure
that the
fuel
D.l3
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