O.S. Engines FS-91S II (P) - Manual (Page 14)

STARTING
The FS-70S 2 , FS-91S 2 and FS-91S 2 -P are not fitted with
manual choke controls, as they are intended for use with an
electric starter only.
A high-torque electric starter not only makes starting the engine
much easier, it dispenses with the need for a choke valve by
turning the engine over fast enough to cause the fuel pump to
prime the cylinder automatically.
Check that the current to the glowplug is switched off.
Check that the polarity of the starter battery leads rotates the
engine counter-clockwise when viewed from the front.
Open the needle-valve 3-3.5 turns from the fully closed
position and temporarily set the throttle in the fully open
position.
Apply the starter and press the starter switch for 5-6
seconds, or until fuel is seen to emerge from the exhaust
outlet, indicating that the cylinder is now primed.
Close the throttle-arm to within 15-20
°
of the fully closed
position and slowly turn the prop "backwards" (clockwise) by
hand approximately 1.5 turns until it is arrested by
compression.This is to enable the kinetic energy of the prop
to subsequently assist the starter through the compression
stroke to start the engine.
Energize the glowplug and apply the starter. If the starter
fails to rotate the engine completely, this may be due to the
cylinder being over-primed, or to the starter battery being
insufficiently charged.
RUNNING-IN ("Breaking-in")
For long life and peak performance, every engine needs
special treatment when new, known as "running-in" or
"breaking-in". This is a process during which the engine is
operated under strictly controlled conditions at the beginning
of its life, in order to avoid the risk of immediate damage to
certain components through becoming overheated or stressed
and to help working surfaces to become smoothed and
aligned for maximum mechanical efficiency thereafter.
With some engines, this can require a tediously protracted
period of bench running, but, as O.S. engines are
manufactured to fine tolerances and from the finest quality
materials, a relatively brief running-in period is sufficient and
can be completed with the engine installed in the aircraft.
The recommended procedure is as follows :
1.
2.
3.
4.
5.
6.
Check these conditions and, instead of pressing the starter
button after applying the starter, have the starter spinning
before applying it to the engine, to give it a "running start".
When the engine starts, slowly open the throttle, leaving
the needle-valve at its rich starting setting to promote cool
running conditions.
However, if the engine slows down because the mixture is
excessively rich, the needle-valve may be closed a little to
speed it up until it runs evenly.
Now disconnect current to the glowplug and gradually close
the needle-valve so that revolutions are increased. Make
adjustments to the needle in small steps. Abrupt changes
at this stage are likely to cause the engine to stall. Restart
the engine by simply applying the starter with the glowplug
re-energized and the throttle at its starting setting.
7.
8.
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