O.S. engine OSM11532 Owner's Instruction Manual page 17

5 Opening and closing of the needle-valve
Turn needle-valve clockwise to close (for leaner mixture).
Turn needle-valve counter-clockwise to open (for richer mixture).
6 Setting the 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
1
2
position.
Needle-valve
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.
Close
Open
16
7 Open the throttle fully
Fully closed position
Fully opened position
8 Priming
Place your finger
over the carburettor
to choke intake.
Turn the propeller
two revolutions
while watching
fuel line.
Close
Open
Throttle
Fuel Tube
Fuel inlet
Fuel will flow
from tank to
carburettor as
propeller is
turned.