O.S. Engines 46LA-S - Manual (Page 19)

Listen to the sound
carefully.
11 Needle-valve adjustment(1)
Then gradually close the needle-valve until the exhaust sound
changes from an irregular pitch (four-cycle) to a steady pitch
(two-cycle).
Close the needlevalve
gradually until the engine
sound is changing from a
four-cycle into a two-
cycle in pitch.
12 Disconnect battery leads
Disconnect the battery leads
from the engine with care so
that the plug clip does not
touch the rotating pro-peller.
If the engine stops when battery leads are disconnected, close
the needle-valve a little (approx. 45˚) further, and restart the
engine.
13 Needle-valve adjustment(2)
As the needle-valve is closed beyond the initial readjustment,
the r.p.m. of the engine will be increased and a continuous
high-pitched exhaust note, only, will be heard.
Key to the needle-valve
adjustment.
(Turn 20-30˚ at a time.)
Turn the needle-valve 20-30˚ in the direction of arrow, and wait
momentarily for the change of r.p.m.
After the r.p.m. of the engine increases, turn the needle-valve
another 20-30˚ 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 20.
18