O.S. Engines FS-40S - Manual (Page 21)

On starting from cold, with the needle-valve
set at the rich starting position:
Take note of this position of the needle-valve.
This will produce the practical best
(i.e. optimum)rpm setting
(lower than maximum rpm).
A light grey exhaust emission may be observed.
Now, re-open needle-valve 20-30
°
maximum rpm is reached and will fall off
(or engine will stop) if needle -valve is closed
any further. Exhaust gas will be very light.
Finally:
revolutions will increase and exhaust
smoke will be reduced.
Further needle-valve closure:
Exhaust smoke will be less dense and
grey in color.
As the needle-valve is closed and the r.p.m. increases
a good deal of white smoke is emitted.
Once the optimum needle-valve setting has been
established (see "Needle-valve adjustment-
Summary") the procedure for starting is simplified as
follows:
1) Open the needle-valve one half-turn (180˚) from
the optimum setting.
2) Open the throttle fully, place your finger over the
carburettor intake and rotate the propeller through
two revolutions to prime the engine.
3) Set the throttle one-third open from the fully closed
position, energize the glowplug and apply the
starter. When the engine starts, re-open the
throttle and re-adjust the needle-valve to the
optimum setting.
Subsequent starting procedure
16
Note: When re-starting the engine on the same
day, provided that atmospheric conditions have
not changed significantly, it may be practicable to
re-start the engine on its optimum (running)
setting. Also, if the engine is being re-started
immediately after a run (i.e.hot), priming should
not be necessary.
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