O.S. engine MAX-91SX-HRING C Spec PS VIPER, Owner'S Instruction Manual

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20
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 High-Speed (Main) 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 Idle Mixture Control Screw
This provides the means of manually adjusting the
60K's mixture control valve. By setting the Mixture
Control Screw for the best idling performance, the
mixture control valve automatically ensures that fuel is
accurately metered to maintain the correct mixture
strength as the throttle is opened.
Two adjustable mixture controls are incorporated in the
Type 60M. They are as follows.
A
B
Idle MIxture Control Screw
High Speed Needle Valve
(Main Needle)
Needle
Adjusting screw
As the idle mixture control screw is applied with LOC-
TITE, at first times it is felt stiff, and it is suggested to
use a littli oversized screwdriver. The screw can be
turned only 90 degrees either way. Do not force to turn
further, or it may break or cause trouble.
NOTE
90 degrees 90 degrees
one-way valve
21
BASIC POSITION OF MIXTURE CONTROL VALVE
(Mixture Control Screw)
Thick
Mixture Control Valve
MIxture Control Screw
Lean
With a model helicopter, adjustments may vary due to
various factors such as climatic conditions, fuel,
muffler, main rotor, weight of the model, gear ratio, etc.
89 degrees
When the triangle mark on the carburetor rotor meets
the far right mark, the throttle is fully closed. When the
triangle mark meets the top mark, the throttle is fully
open. The range is 89 degrees. You may use the other
three marks as the reference marking of throttle
opening to your preference when hovering.
WARNING!
Never try to check the triangle mark position while
the engine is running and rotor is
rotating, or you may be hit by rotating rotor which
results in serious injury. Stop the engine and rotor
before checking the triangle mark position.
Graduations on the carburetor body
Carburetor Rotor
Carburetor Body
Fully closed
position
Fully opened position
HEX KEY NEEDLE ADJUSTMENT
The knurled head of the main needle valve (High-Speed)
is 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.
As delivered, the Mixture
Control Screw is positioned
at the center as shown in the
sketch. Mixture gets lean
when the Mixture Control
Screw is turned right, while
mixture gets rich when the
Mixture Control Screw is
turned left.
Therefore, the Mixture Control Screw position will
vary with each model and set- up, and it is normal if
the Mixture Control Screw position is off center.
As shown in the sketch,
the carburetor has
graduation marks.