O.S. Engines FL-70 - Manual (Page 13)

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The FL-70 is supplied with an O.S. Type F glowplug,
specially designed for O.S. four-stroke engines.
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.
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.
However, plug life can be extended and engine
performance maintained by careful use, i.e.:
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.
Glowplug life
Particularly in the case of very high performance
engines, glowplugs must be regarded as expendable
GLOWPLUG
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Two adjustable controls are provided on this
carburettor.
They are as follows:
TYPE 60W CARBURETTOR
The Airbleed Screw
This is used to establish the mixture strength
required for steady idling and a smooth
transition to medium speeds. (The varying
mixture strength required between part-
throttle and full-throttle running is
automatically adjusted by coupled movement
of the throttle.)
The sequence in which these controls are
adjusted is explained in the succeeding
sections, under Starting, Running-in and Idling
Adjustment.
Needle Valve
Airbleed Screw
The Needle Valve
This is used to establish the
fuel/air mixture strength
required for full power when
the throttle is fully open.
STARTING
The FL-70 is not equipped with manual
choke controls, as it is intended for use
with an electric starter only.
A high-torque electric starter not only
makes starting the engine easier, it
dispenses with the need for a choke valve
by turning the engine over fast enough to
cause the fuel pump to prime the cylinder
automatically.
Starting procedure is as follows:
Fill the fuel tank with fuel. When filled,
prevent fuel flowing into the carburetor with
a commercially available fuel stopper, etc.
Release the stopper before starting the
engine.
Make sure that plug element glows red, and
install the plug in the cylinder head.
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