O.S. engine MAX-75AX Instruction Manual page 15

4. During subsequent flights, the needle-valve
can be gradually closed to give more power.
However, if the engine shows signs of
running too lean, the next flight should be
set richer. After a total of ten flights, the
engine should run continuously, on its
optimum needle-valve setting, without loss
of power as it warms up.
After the completion of the running-in adjust
5.
the carburetor at optimum setting referring
to MIXTURE CONTROL
ADJUSTMENT section and SUBSEQUENT
READJUSTMENT section.
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.
Optimum needle setting(1)
Slowly advance the throttle to its fully open
position, then gradually close the needle-valve
until the exhaust note begins to change. (4-
cycle to 2-cycle)
Optimum needle setting(2)
As the needle-valve is closed slowly and grad-
ually, the engine r.p.m. will increase and a
continuous high-pitched exhaust note, only,
will be heard. Close the needle-valve 10-15
VALVE
degrees and wait for the change of r.p.m.
After the engine r.p.m. increases turn the nee-
dle-valve another 10 -15 degrees 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.
28
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
engine is running rich.
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.
29
Note :
This diagram is for reference
purposes only.
Actual needle positions may
differ from those shown.
while the