Mixture Controls; Glowplug - O.S. engine MAX-75AX-BE Instruction Manual

Two mixture controls are provided on this
Carburetor.
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.
The Mixture Control Valve
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.
An O.S. BE-3 glowplug is supplied with
the engine. Use only the O.S. BE-3 as
replacement. Carefully install plug finger-
tight, before final tightening with the
correct size plug wrench.
The role of the glowplug
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.

MIXTURE CONTROLS

Mixture Control Valve of the carburetor is set at
basic position ( a little on the rich side) at the
factory. However, minor readjustment will be
required for atmospheric conditions and a
model. When a good result is not obtained with
the factory setting, readjust it according to the
MIXTURE CONTROL VALVE ADJUSTMENT
section. 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.
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GLOWPLUG

Glowplug life
Be sure to disconnect the plug leads when
adjusting the needle-valve at higher r.p.m. range.
Do not run the engine too lean and do not leave the
battery connected while adjusting the needle.
When to replace the glowplug
Apart from when actually burned out, a plug may
need to be replaced because it no longer delivers its
best performance, such as when:
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.
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Needle Valve
Mixture Control Valve