Chapter 7: Ignition System
72
About the spark plug
• The spark plug is a Torch model F6RTC, gapped
to .024”-.032” (.60-.80 mm).
• Champion RN14YC or NGK BPR4ES are physi-
cally similar but do not match the F6RTC in heat
range. This difference in heat ranges will effect
performance and emissions. It is recommended
that the Torch F6RTC plug be used for service.
• Wear rate will vary somewhat with severity of
use. If the edges of the center electrode are
rounded-off, or any other apparent wear / dam-
age occurs, replace the spark plug before oper-
ating failure (no start) occurs.
Cleaning the spark plug
• Cleaning the spark plug is not recommended. If
the plug needs to be cleaned, replace it.
• Use of a wire brush may leave metal deposits on
the insulator that cause the spark plug to short-
out and fail to spark.
• Use of abrasive blast for cleaning may damage
the ceramic insulator or leave blast media in the
recesses of the spark plug. When the media
comes loose during engine operation, severe
and non-warrantable engine damage may result.
Inspection of the spark plug
Inspection of the spark plug can provide indications of
the operating condition of the engine.
• Light tan colored deposits on insulator and elec-
trodes is normal.
• Dry, black deposits on the insulator and elec-
trodes indicate an over-rich fuel / air mixture (too
much fuel or not enough air)
• Wet, black deposits on the insulator and elec-
trodes indicate the presence of oil in the com-
bustion chamber.
• Heat damaged (melted electrodes / cracked
insulator / metal transfer deposits) may indicate
detonation.
• A spark plug that is wet with fuel indicates that
fuel is present in the combustion chamber, but it
is not being ignited.
Spark plug removal
1. Disconnect and ground the spark plug wire.
2. Remove the spark plug using a 13/16” or 21mm
wrench. A flexible coupling or “wobbly” exten-
sion may help. See Figure 7.14.
3. Gap a new spark plug to .024”-.031” (.60-.80
mm).
4. Install the new spark plug and tighten to a torque
of 15 - 18.5 ft - lbs (20-25 Nm).
Figure 7.14
Spark plug hole
High tension lead
Muffler
(plug removed)
Valve cover
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