Electrical; Checking The Spark Plug; Checking The Ignition Timing - Yamaha YZ125 2009 Owner's Service Manual

ELECTRICAL

CHECKING THE SPARK PLUG

1. Remove:
• Spark plug
2. Inspect:
• Electrode "1"
Wear/damage → Replace.
• Insulator color "2"
Normal condition is a medium to light tan
color.
Distinctly different color → Check the engine
condition.
When the engine runs for many hours at low
speeds, the spark plug insulator will become
sooty, even if the engine and carburetor are in
good operating condition.
3. Measure:
• Plug gap "a"
Use a wire gauge or thickness gauge.
Out of specification → Regap.
Spark plug gap:
0.6–0.7 mm (0.024–0.028 in)
Standard spark plug:
BR9EVX/NGK (resistance type)
4. Clean the plug with a spark plug cleaner if
necessary.
5. Tighten:
• Spark plug
Spark plug:
20 Nm (2.0 m•kg, 14 ft•lb)
• Before installing a spark plug, clean the gas-
ket surface and plug surface.
• Finger-tighten "a" the spark plug before torqu-
ing to specification "b".

CHECKING THE IGNITION TIMING

1. Remove:
• Fuel tank
Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section in the CHAPTER 4.
• Spark plug
• Crankcase cover (left)
2. Attach:
• Dial gauge "1"
• Spark plug hole dial stand "2"
Dial gauge:
YU-3097/90890-01252
Spark plug hole dial stand:
YU-1256
3. Rotate the magneto rotor "1" until the piston
reaches top dead center (TDC). When this
happens, the needle on the dial gauge will
stop and reverse directions even though the
rotor is being turned in the same direction.
4. Set the dial gauge to zero at TDC.
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ELECTRICAL