MTD 61 series, Shop Manual

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Ignition System
91
About the spark plug
• The spark plug is a F6RTC, part #951-10292, gapped to 0.024” - 0.031” (0.6 - 0.8 mm).
NOTE: The X65 engine uses a F5RTC, part #951-14437, gapped to 0.024” - 0.031” (0.6 - 0.8 mm).
• Wear rate will vary somewhat with severity of use. If the edges of the center electrode are rounded-off, or
any other apparent wear / damage occurs, replace the spark plug before operating 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 electrodes is normal.
• Dry, black deposits on the insulator and electrodes indicate an over-rich fuel / air mixture (too much fuel or
not enough air)
• Wet, black deposits on the insulator and electrodes indicate the presence of oil in the combustion cham-
ber.
• 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” extension
may help. See Figure 7.14.
3. Gap a new spark plug to 0.024” - 0.031” (0.60 - 0.80
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