Tuning Conditions; Tuning Procedure - Rolls-Royce Silver Shadow Workshop Manual

Workshop Manual
Rolls Royce Silver
Chapter K
synchronised, the full throttle stop screw is adjusted
and the linkage clearance is correct as described under
Carburetter-To set.
Tuning conditions
To ensure that the engine temperature and mixture
requirements are stabilised, tuning must be carried out
in accordance with the following setting cycle.
1. Set the volume screws fully in, then back off 14
turns.
2.
With the carburetter dampers, suction chambers,
springs and pistons already removed to enable the
throttle synchronisation to be checked, set the main jet
screw as follows.
Using special spanner (RH 8050), slacken the car-
buretter jet screw lock-nuts then manipulate each jet
screw until the jet in each carburetter body is level with
its bridge piece.
Screw down the jet screw 2 turns.
3. Check that the lower face of the annular groove
in the needle is level with the piston base (see Fig. K17).
4. Check that the piston is free to slide in its suction
chamber.
5. Fit the air valve pistons, springs and suction
chambers in a clean dry condition then top-up the
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 chamber and air valve piston
should be fitted to the carburetter from which it was
removed.
Do not fit the damper at this stage.
6. If a hot idle compensator valve is fitted remove
the pipe from the hot idle compensator valve connec-
tion marked 'OUT'. Blank off the pipe.
7. Connect an electric impulse tachometer in
accordance with the manufacturer's instructions.
8. Warm-up the engine at fast-idle speed until the
normal operating temperature is attained. Preferably
this should be carried out with the car standing in an
ambient temperature of between 16°C. and 27°C.
(60°F. and 80°F.). Run the engine for at least five
minutes after the thermostat has opened; the thermo-
stat opening point can be detected by a sudden rise in
temperature of the thermostat elbow pipe or by
reference to the coolant temperature gauge (if fitted).
9. If a refrigeration system is fitted, ensure that the
system is switched off.
10. 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.
Shadow 6 Bentley T Ser~es
Tuning procedure
11. Tuning operations may now be commenced and
must be carried out in the shortest time possible. If
the time for setting exceeds a three minute period, open
the throttle and run the engine at 2 000 r.p.m. for
t
minute to purge the system tfien resume tuning.
Repeat this clearing operation if further periods of
three minutes are exceeded.
Immediately after a clearing operation when the
engine is at idle speed, the suction chamber should be
tapped all the way round with a light weight, non-
metallic instrument (e.g. the wooden handle of a screw-
driver) to eliminate piston hysteresis (see Fig. K23).
12. Ensure that Neutral is selected on the gear range
selector.
13. Set the idle speed to 600 r.p.m. by adjusting the
fixed throttle stop screw.
14. Run the engine at idle speed then balance the car-
buretters using the volume screws, the carburetters are
balanced when the hiss heard at the small drilling
in the neck of each suction chamber is of
equal intensity. The volume screws should only be
adjusted within the range fully closed to two complete
turns open, otherwise an obtrusive whistle from the
carburetters may result. Fit the dampers.
15. Turn both jet adjusting screws by equal amounts
in the same direction, approximately
4
of a turn at a
time until the maximum r.p.m. is recorded on the
tachometer.
Note Turning the screw clockwise richens the
mixture, conversely, turning the screw
anti-clockwise weakens the mixture.
16. Set the mixture balance on each carburetter
individually using the jet adjusting screw approxi-
mately Q of a turn at a time in either direction until the
maximum r.p.m. is obtained.
17. Turn both jet adjusting screws
by
equal amounts
anti-clockwise (weaker mixture) until the engine speed
just commences to fall, then turn both adjusting screws
4
of a turn clockwise (richer mixture) and tighten the
lock-nuts using spanner (RH 8050).
18. Check the idle speed and if necessary adjust to
the original speed (see Operation 13).
19. Check that the carburetters are balanced by
raising and releasing each carburetter piston lift pin in
turn then comparing engine response. The carburetters
are balanced if the response is the sar;:: for each
carburetter. If the carburetters are not balanced repeat
Operations 13 to 18 inclusive until a satisfactory
balance is obtained.
In certain countries the exhaust C.O. must be
checked. If these regulations apply Operation 20 to 24
inclusive should be carried out.
20. Purge the engine at 2 000 r.p.m. in Neutral for a
period of
f
minute.