Checking The Spark Plug - Yamaha MT125 Owner's Manual

Checking the spark plug

The spark plug is an important engine
component, which is easy to check.
Since heat and deposits will cause any
spark plug to slowly erode, the spark
plug should be removed and checked
in accordance with the periodic main-
tenance and lubrication chart. In addi-
tion, the condition of the spark plug
can reveal the condition of the engine.
To remove the spark plug
1. Remove the spark plug cap.
1. Spark plug cap
2. Remove the spark plug as shown,
with the spark plug wrench includ-
ed in the owner's tool kit.
PERIODIC MAINTENANCE AND ADJUSTMENT
EAU19605
1. Spark plug wrench
To check the spark plug
1. Check that the porcelain insulator
around the center electrode of the
spark plug is a medium-to-light
tan (the ideal color when the vehi-
cle is ridden normally).
TIP
If the spark plug shows a distinctly dif-
ferent color, the engine could be oper-
ating improperly. Do not attempt to
diagnose such problems yourself. In-
stead, have a Yamaha dealer check
the vehicle.
2. Check the spark plug for electrode
3. Measure the spark plug gap with a
ZAUM0037
1. Spark plug gap
6-9
erosion and excessive carbon or
other deposits, and replace it if
necessary.
Specified spark plug:
NGK/CR9E
wire thickness gauge and, if nec-
essary, adjust the gap to specifi-
cation.
1
Spark plug gap:
0.7–0.8 mm (0.028–0.031 in)
6