28
MAN-028
13- SPARKPLUG AND THERMAL DEGREE
The engine is supplied with a standard NGK BR10EG sparkplug which represents a
good compromise between the needs of a good break-in and the racing needs in
normal conditions.
Use of different sparkplugs is possible and, as a general information, we are
attaching a correspondence list among sparkplugs of other brands based on thermal
degree which represents the capacity of the sparkplug to dissipate the internal heat.
The colour of the various parts of the sparkplug more exposed to the combustion
flames gives a good indication on the adequacy of the thermal degree and on the
carburetion. It is necessary though to understand which of the two parameters has to
be changed and only the experience tells how to identify the most proper thermal
degree of a sparkplug as lean or rich mixtures can generate the same final look
which can also be achieved with a hot or cold sparkplug.
See table:
An excessively warm sparkplug shows the
symptoms listed aside
ATTENTION:
Always use a warmer than standard spark
plug with cold or rainy climates.
Extremely clear color, porous lock and calcification of
the electrodes and of the internal insulation.
Irregularities in the ignition, preignition and
detonation with tendency to perforate the top of the
piston.
Note:
Some of these symptoms can be achieved
with lean mixtures.
A correct thermal degree shows:
Colour of the insulator end from yellow grey to dark
brown for mixtures respectively lean or rich.
An excessively cold sparkplug shows the
symptoms, listed aside.
ATTENTION:
Always use a colder than standard
sparkplug with hot climates.
Insulator end and electrodes covered with black
shady soot.
Ignition difficulties.
Note:
a wet or oily electrode could also mean an
excessively rich mixture.
COMPARISON TABLE BASED ON
THE THERMAL DEGREE
HOT
BOSCH NGK CHAMPION
WO8CS BR9EG N54R
WO7CS BR10EG N52R
WO6CS BR11EG
COLD
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