O.S. Engines FS-40S - Manual (Page 23)

These engines are equipped with a throttle type car-
burettor which provides a wide range of engine speed
control. With the throttle lever linked to a suitable
servo in the model, movement of the throttle control
on the transmitter will enable engine to be varied,
proportionally, from idling speed to full power.
The carburettor of your engine has been factory set
for the approximate best results and no adjustment
(except to the needle-valve) should be required
provided that the fuel tank is correctly located, as
previously described. After the engine has been run-
in, check the operation of the throttle according to the
following chart. Re-adjust the controls only when
necessary.
CARBURETTOR
22