O.S. Engines 25LA - Manual (Page 21)

16 Disconnect battery leads
Disconnect the battery
leads from the engine
with care so that the
plug clip does not touch
the rotating propeller.
If the engine stops when battery leads are disconnected,
close the needle-valve a little (approx. 30˚) further, and restart
the engine.
17 Needle-valve adjustment(2)
As the needle-valve is closed beyond the initial readjustment,
the rpm of the engine will be increased and a continuous high-
pitched exhaust note, only, will be heard.
Key to the needle-valve
adjustment.
(Turn 10-15˚ at a time.)
Turn the needle-valve 10 -15˚ in the direction of arrow, and
wait momentarily for the change of r.p.m.
After the rpm of the engine is increased, turn the needle-valve
another 10 -15˚ and wait for the next change of r.p.m.
As the speed of the engine does not instantly change with
needle-valve readjustment, small movements, with pauses
between, are necessary to arrive at the optimum setting.
IMPORTANT NOTE
When fine-tuning the needle-valve to reach peak per-
formance, take care not to run the engine too lean
and cause it to overheat.
Be sure to observe the simple running-in procedures
described on Page 22.
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