O.S. engine FS-40S-C Owner's Instruction Manual page 17

After running the engine for four or five tanks
of fuel, begin closing the needle 5-15 degrees
between succeeding runs. Also, vary its
speed, from idling to medium RPM, with the
throttle. See sketch.
Eventually, the engine will begin to loosen up
sufficiently to allow short bursts of full-throttle
acceleration with the needle-valve at its
optimum setting.
Note!
Do not close the needle-valve any further. If
you do so, the engine will begin to overheat
and the car will slow down, accompanied by
visibly diminished exhaust smoke. In this
event, bring the vehicle to a halt immediately
and reopen the needle-valve 10° to 20°.
Now open the needle-valve 10°-20° from the
setting at which the highest straight line
speed is obtained. This slightly rich setting
should provide the optimum balance. Run
the car for about three more tanks of fuel to
allow fine-tuning of any final adjustments.
Re-adjust the
neccessary, so that the car may not move at
idling.
Needle Slot
The position of the
needle-valve where
highest speed of
the vehicle is
obtained.
Optimum needle-valve position (10° to 20° opened
from the position where highest speed of the vehicle
is obtained.)
To stop the engine, close the throttle to idling
speed, then shut it off completely with the
trim lever on the transmitter. To cut off the
fuel supply, pinch the fuel delivery tube to the
carburettor.
16
throttle stop screw,
The position of the
needle-valve when
starting the engine.
Close the needle-valve
approx. 30° after
running the vehicle for
one full tank of fuel.
Repeat this procedure
several times.
if