O.S. Engines 46FX-H Ring - Manual (Page 13)

CARBURETOR CONTROLS
With a fixed-wing model, power failure is rarely a
serious threat to the safety of the aircraft since it can
usually glide down to a safe landing. In a helicopter,
on the other hand, it is vitally imporant that the engine
keeps running and that there is a quick and reliable
response to the throttle in order to ensure safe ascent
and descent of the model.
The Needle Valve:
When set to produce maximum power at full throttle,
this establishes the basic fuel/air mixture strength.
This is then maintained by the carburetor's
automatic mixture control system to cover the
engine's requirements at reduced throttle settings.
The Mixture Control Valve (Mixture ControlScrew):
For adjusting the mixture strength at part-throttle
and idling speeds, to obtain steady idling and
smooth acceleration to medium speeds. The Mixture
Control Valve has been factory set for the
approximate best result. First, run the engine as
received, and re-adjust the Mixture Control Valve
only when necessary.
Two adjustable controls are provided on this carburetor.
Needle Valve
Throttle Lever
Mixture Control Valve
(MIxture Control Screw)
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RE-ESTABLISHMENT OF MIXTURE CONTROL
VALVE SETTING
In the course of making carburetor adjustments, it is
just possible that the Mixture Control Valve may be
inadvertently screwed in or out too far and thereby
moved beyond its effective adjustment range.
Its factory setting can be reestablished as follows;
Disconnect the throttle linkage by removing the
control rod from the throttle lever.
Fully close the throttle.
Turn the Mixture Control Valve clockwise gently
until it stops, while keeping the throttle fully closed.
Do not over-tighten the valve.
Turn the Mixture Control Valve 2-1/2 turns counter-
clockwise from the above position. This is the
basic (factory) setting.
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