O.S. Engines FS-91 II FI - Manual (Page 20)

20
GLOWPLUGS
The role of the glowplug
Glowplug life
Particularly in the case of very high performance engines, glowplugs must be regarded as
expendable items.
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.:
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.
Since the compatibility of glowplug and fuel may have a marked effect on performance and
reliability, it may be worthwhile to choose the R/C type plug found most suitable after tests.
O.S. TYPE F plug is supplied with the engine. Recommended O.S. plug Type F is suitable to use for richer
mixture. Carefully install plug finger-tight, before final tightening with the correct size plug wrench.
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.