O.S. Engines FS-91S II (P) - Manual (Page 19)

Do not leave unused fuel in the engine at the conclusion of a
day's flying. Accepted practice is to cut off the fuel supply
while the engine is still running - at full throttle - then, expel
as much fuel residue as possible by turning the engine over
for 5-10 seconds with the electric starter.
Finally, inject some after-run oil through the glowplug hole and
turn the engine over several times by hand.
When the engine is not to be used for some months (for
example, as between flying seasons) a worthwhile precaution
is to remove it from the airframe and, after washing off the
exterior with alcohol (not gasoline or kerosene) to carefully
remove the fuel pump, carburettor with intake pipe and all
silicone tubes and put them safely aside.
Make sure that the engine is reasonably clean externally, then
remove the glowplug and immerse the engine in a container
of kerosene. Rotate the crankshaft while the engine is
immersed. If foreign matter is visible in the kerosene, rinse the
engine again in clean kerosene, before removing it, vigorously
shaking off the excess and wiping it dry.
CARE & MAINTENANCE (laying up)
The fuel pump assembly, carburettor/pressure-regulator and
silicone tubes must be cleansed separately in methanol or
glow fuel. On no account must they come into contact with
kerosene.
Before completely reassembling the engine, make sure that
no kerosene remains inside that could find its way into the
pump unit, carburettor, etc. Inject, sparingly, preserving oils,
rust inhibitors, etc. unless approved for silicone-rubber
products.
An appropriate alternative here may be one of the high-quality
synthetic lubricating oils.
Finally, seal the engine in a heavy polyethylene bag until
required for refitting to the airframe.
Debris tends to
accumulate in
this area
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