O.S. Engines 61RX-H WC - Manual (Page 14)

The Medium Speed Needle Valve
This is an extra control that can be brought into
play, if necessary, after adjusting A and B above. It
provides the means of fine-tuning mixture strength
over that all-important part of a helicopter's throttle
range where the model is flying in, or near, the
hovering mode. C
STARTING
Close
Open
Be sure to use a muffler pressurized fuel feed. Use
the same fuel as you intend to employ for actual
operation of your model.
1.
2.
Opening and closing of the Needle-Valve
Turn the needle clockwise to
close the needle-valve, and turn
the needle counter-clockwise to
open the needle-valve as shown
in the sketch.
High Speed needle-valve:
exactly two turns open from the fully closed
position.(Note: If a different muffler is used, this
setting may require readjustment)
Idle Mixture Control Screw:
exactly two turns open from the fully closed
position.
exactly one turns open from the fully closed
position.
Medium Speed needle-valve:
Idle MIxture Control Screw
High Speed Needle Valve
(Main Needle)
Medium Speed Needle Valve
HEX KEY NEEDLE ADJUSTMENT
The knurled heads of the two needle valves (High-Speed
and Medium Speed) are provided with diagonal slots for
use with a screwdriver. Alternatively, formore positive
location via an Allen hexagonal key, these heads also
have M2.6 internal threads, into which M2.6x5mm Allen
cap-head screw may be fitted. To avoid risk of damage
to the fuel passages when tightening these screws,
remove the needle valves from the carburetor and use
'Loctite' thread-lock compound to secure the screw.
13