O.S. Engines 21XZ-M - Manual (Page 8)

14
As the idle mixture control screw is
installed with LOCTITE, it may ini-
tially feel stiff, and it is suggested
to use a little larger screwdriver.
The screw can be turned only 90 degrees either way. Do
not force it to turn further, or it may break end cause
trouble.
NOTE 90 degrees 90 degrees
Type 20G Remote-mounting
Needle Valve Assembly (Optional parts)
It enables the Needle Valve to be installed separately
from the engine in a position where (especially with a
cowled or enclosed engine) it may be more accessible
for adjustment. (See sketch.) Install as follows:
Remove the needle-valve holder from the
carburetor and fit the plug screw in its place.
Drill a 6mm dia. hole in the required position
on the model and insert the Remote Needle
Valve Assembly. If necessary, install a suitable
mounting plate in the model to which the
Remote Needle Valve Assembly may be fitted.
You may also use the
Needle Control Lever in
conjunction with the Re-
mote-mounting Needle
Valve Assembly.
lock nut Ratchet spring
Needle
Remote needle holder Model or fitting plate
Tube length should be kept as short as
possible.
Remote needle holder
Remote needle nut
Plug screw
Silicone tubing
Needle valve
control lever
15
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. RP7 plug when it is
necessary to replace. Carefully install
plug finger-tight, before final tightening
with the correct size plug wrench.