O.S. Engines 18TM Revo - Manual (Page 23)

Finally, beyond the nominal break-in period,
a slight readjustment toward a leaner needle
setting may be required to maintain
maximum performance.
The correct functioning of the carburetor
depends on its small fuel orifices remaining
clear.
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 Throttle Lever body.
First rotate the Mixture
Control Valve until its
slotted head is flush with
the carburetor body.
Then screw the valve in
exactly 0.5 turn. This is
the standard position.
Mixture Control Valve
Carburetor Body
Rotate the Metering
Needle until its slotted
head is flush with the
Throttle Lever body.
This is the standard
position.
Throttle Lever Carburetor Body
Slide Valve Metering Needle
22