O.S. engine max-12TZ series Owner's Instruction Manual page 12

With the optimum mixture control position,
light smoke is visible during high speed
running,and the engine rpm increases
smoothly during acceleration. Remember
that, if the engine is operated with the fuel/air
mixture slightly too lean, it will overheat and
run unevenly. As with all engines, it is
advisable to set both the needle-valve and
metering needle slightly on the rich side of
the best rpm setting, as a safety measure.
If the engine runs too fast with the throttle
closed, the throttle stop screw should be
turned counter-clockwise to allow the throttle
opening to be reduced.
Finally, beyond the nominal break-in period,
a slight readjustment toward a leaner needle
setting may be required to maintain
maximum performance.
REALIGNMENT OF METERING NEEDLE AND
MIXTURE CONTROL VALVE
In the course of making carburetor
adjustments, it is just possible that the
Metering Needle and the Mixture Control
Valve may be inadvertently screwed in or out
too far and thereby moved beyond its
effective adjustment range.
The basic positions can be found by rotating
the Metering Needle until its slotted head is
flush with the ball link body.
22
Carburetor Body
Slide Valve
Rotate the Mixture Control
Valve until its slotted head is
flush with the carburetor
body. This is the basic
position.
Mixture Control Valve
Carburetor Body
23
Ball Link
Rotate the Metering
Needle until its slotted
head is flush with the
ball link body. This is the
basic position.
Metering Needle