Workshop
Manual
Rolls Boyce
Silver Shadow
4
Bentley
T
Series
Chapter
K
FIG.
K22 CHECKING THE FLOAT CHAMBER
DEPRESSION
1
Rule
2
Pressure
tapping
3
'A'
bank float chamber
4
Manometer
screw until the jet in each carburetter body is level
with the bridge piece (see
Fig.
K19).
Screw down the jet screw
2&
turns.
Fit the air valve pistons, springs and suction
chambers in a clean dry condition then top-up each
damper piston with the approved oil; the oil level
should be approximately
4
in. (12,7 mm.) below the
top of the piston rod, do not overfill.
It
is
important that each suction chamber and air
valve piston should be returned to the carburetter from
which
it
was removed.
Do not fit the damper at this
stag.
3.
Connect an electric impulse tachometer in accord-
ance with the manufacturer's instructions.
4.
Warm the engine at 'fast-idle' speed until normal
operating temperature is attained. Run the engine for
at least five minutes after the thermostat has opened;
the thermostat opening point can be detected by a sud-
den rise in temperature of the thermostat elbow pipe
or by reference to the coolant temperature gauge.
Note It is important that the engine tuning is
carried out only after the engine tem-
perature has stabilised and at an ambient
temperature of between 16°C. and 27°C.
(60°F. and 80°F.).
During the warm-up period, Operations 5,
6
and 7
should be carried out.
5. Ensure that the refrigeration system is switched
off.
6. Check that the choke butterfly valve is
fully open
by feeling the tension at the operating levers and hear-
ing it snap back on its stop when any tension which
has been applied is released.
7.
Remove the cap from the pressure tapping on
'A'
bank carburetter float chamber then connect a mano-
meter to the tapping (see
Fig.
K22). The manometer
must be capable of measuring 6 in.
(15,25 cm.) of
water level difference.
8.
Run the engine in Neutral at 2 000 r.p.m. for
f
minute to purge the system. During this period check
the manometer reading; this reading should show
between
24 in. and
34-
in.
(6,99
cm. and 8,25 cm.)
difference in water level.
If
this reading is not readily
attained the system should be checked as follows.
A
low or zero reading may be caused by
(a) An obstruction in one or more of the following:
The engine side of the weakener unit.
Weakener unit to weakener cut-off valve pipe.
Vacuum take-off plate to weakener cut-off
valve pipe.
Vacuum take-off plate.
FIG. K23 TAPPING THE NECK
OF
THE SUCTION
Pressure tapping on
'A'
bank carburetter
CHAMBER
float chamber.
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