O.S. Engines 25LA - Manual (Page 17)

Close
Open
Needle-valve
Open the needle-valve 4 turns(for 10LA), 3 turns (for 15LA),
1 turns (for 25LA) in the direction of arrow from the closed
position.
2
1
Fully closed position
Fully opened position Throttle
Close
Open
Fuel inlet
Fuel Tube
Fuel will flow
from tank to
carburettor as
propeller is
turned.
Place your finger
over the carburettor
to choke intake.
Turn the propeller
two revolutions
while watching
fuel line.
5 Opening and closing of the needle-valve
6 Setting the needle-valve
Turn needle-valve clockwise to close (for leaner mixture).
Turn needle-valve counter-clockwise to open (for richer mixture).
The position where the needle-valve stops is the fully closed
position. It may be convenient to remember the position of the
mark or set-screw at this time.
7 Open the throttle fully
8 Priming
16