20
With each successive flight, close the needle-valve very
slightly until, at the end of about 10 flights, the needle is set
for full power. Do not "over-lean" the mixture in an attempt
to extract more power.
8.
If overheating should be suspected at any time during
flight (i.e.if the engine begins to "labor") reduce power by
partially closing the throttle and land the aircraft to
enable the needle-valve to be readjusted to a richer
setting.
Following the initial running-in session, check for any
looseness in the installation due to vibration, then allow the
engine a period of moderately rich operation in flight.
6.
For the first flight, have the needle-valve set on the rich
side and adjust the throttle trim on the transmitter so that
the engine does not stop when the throttle is closed to the
idle setting.
7.
Note:
Remember that, when the engine is not yet fully run-in,
the carburettor cannot be expected to give its best
response in flight. Abrupt operation of the throttle, for
example, may cause the engine to stall. Therefore, at this
time ,the aircraft should, as far as is possible, be flown at
an altitude sufficient to enable an emergency landing to
be safely made if the engine stops.
Once the engine has demonstrated that it can be safely
operated at full power, the carburettor can be adjusted for
optimum throttle response, following the instructions given
in the next section.
9.
21
In the course of making carburetor adjustments, it is just
possible that the Mixture Control Valve setting may be
upset.
Its basic setting can be re-established as follows:
First, set the throttle lever at fully closed position.
Turn the Mixture Control Valve counter-clockwise until it
stops, then screw it out 3 turns. This is the basic position.
REALIGNMENT OF MIXTURE CONTROL VALVE
Start the engine, open the throttle fully and set the needle-
valve slightly rich (45-60
°
) from the highest r.p.m. setting.
Close the throttle to the idle position. Allow the engine to
idle for about 5 seconds, then reopen the throttle. The
engine should accelerate smoothly back to full speed.
If, instead, the engine responds sluggishly and emits an
excess of white smoke from the exhaust, the idle mixture is
too rich. Turn the mixture control valve approx. 45
°
clockwise to lean the idling mixture.
On the other hand, if the engine hesitates before picking up
speed or even ceases firing completely, the idle mixture is
likely to be too lean. Turn the mixture control valve 90
°
counter-clockwise to substantially enrich the mixture, then
back again 45
°
clockwise.
IDLE MIXTURE ADJUSTMENT
1.
2.
3.
4.
In paragraphs 3 and 4 above, the 45
°
total movements are,
of course, approximate. It will be necessary to fine-tune the
mixture control screw 10-15
°
at a time to reach the best
setting for optimum throttle response.
Continue re-checking the idle mixture setting until the
engine responds smoothly and positively to operation of
the throttle at all times.
5.
6.
VALVE ADJUSTING
Valve clearances are correctly set before any O.S. engine
leaves the factory and, in normal use, will seldom require
adjustment. However, if, after a considerable amount of
running time, a loss of power is detected, or if he engine
has been disassembled for repair, these clearances
should be checked and reset as necessary.
For checking and adjusting the valve clearances, a VALVE
ADJUSTING TOOL KIT is available as an optional
accessory. Also, a 5.5mm wrench (not supplied) is
required for this purpose.
• Wrench 5.5mm
• Feeler gauge 0.04mm
The kit comes in a plastic case and includes:
(Code No.72200060)
• Feeler gauge 0.1mm
• Hex. key 1.5mm
• Wrench 5mm
