16
MIXTURE CONTROLS
The Needle Valve
When set to produce maximum power at full
throttle, this establishes the basic fuel/air
mixture strength. The correct mixture is then
maintained by the carburetor's built-in automatic
mixture control system to cover the engine's
requirements at reduced throttle settings.
Two mixture controls are provided on this
Carburetor.
Needle Valve
Mixture Control Screw
Mixture Control Screw of the carburetor is set
at basic position ( a little on the rich side) at the
factory. However, minor readjustment will be
required for a fuel used, atmospheric
conditions and a model. Please note during a
running-in period flights should be made with a
slightly rich needle setting. Therefore, during a
running-in period proper carburetor responses
will not be obtained. Adjust it at optimum
position after the running-in is completed.
Throttle Stop Screw
The Mixture Control Screw
This meters fuel flow at part-throttle and idling
speeds to ensure reliable operation as the
throttle is opened and closed. The Mixture
Control Valve is factory set for the approximate
best result. First run the engine as received and
readjust the Mixture Control Screw only if
necessary.
17
GLOWPLUG
The role of the glowplug
Glowplug life
Particularly in the case of very high performance
engines, glowplugs must be regarded as expendable
items. However, plug life can be extended and engine
performance maintained by careful use, i.e.:
Install a plug suitable for the engine.
Use fuel containing a moderate percentage of
nitromethane unless more is essential for racing events.
Do not run the engine too lean and do not leave the
battery connected while adjusting the needle.
With a glowplug engine, ignition is initiated by the
application of a 1.5-volt power source. When the
battery is disconnected, the heat retained within the
combustion chamber remains sufficient to keep the
plug filament glowing, thereby continuing to keep the
engine running. Ignition timing is 'automatic' : under
reduced load, allowing higher rpm, the plug becomes
hotter and, appropriately, fires the fuel/air charge
earlier; conversely, at reduced rpm, the plug become
cooler and ignition is retarded.
Apart from when actually burned out, a plug may
need to be replaced because it no longer delivers its
best performance, such as when:
When to replace the glowplug
Filament surface has roughened and turned white.
Filament coil has become distorted.
Foreign matter has adhered to filament or plug
body has corroded.
Engine tends to cut out when idling.
Starting qualities deteriorate.
Since the compatibility of the glowplug
and fuel may have a marked effect on
performance and reliability, it is suggested
to use the O.S. Type F plug when it is
necessary to replace. Carefully install
plug finger-tight, before final tightening
with the correct size plug wrench.
