O.S. engine MAX-91FX Owner's Instruction Manual page 22

Needle-valve adjustment diagram
Practical best(optimum) needle-valve setting
6
Clear, high-pitched two-stroke
exhaust note
5
Intermittent, high-pitched
two-stroke note
superimposed
on low "four-stroke"
sound.
4
Disconnect battery
leads from glowplug at
about this point.
3
Exhaust note starts to change.
Note: Although this is a two-stroke engine it fires like a
four-stroke at these rich needle-valve settings-i.e. ignition
of the fuel charge takes place at every fourth stroke of the
piston instead of at every second stroke.
7
Maximum rpm
setting("Lean").
1
STARTING
"Rich" needle-valve
setting when starting
the engine.
2
The engine may stop if
the battery leads are
disconnected from the
glowplug while the
engine is running rich.
21
Note :
This diagram is for reference
purposes only.
Actual needle positions may
differ from those shown.
To stop the engine, close the
•
throttle completely to cut off
fuel/air supply.