Checking The Spark Plug - Yamaha SR400 Owner's Manual

Periodic maintenance and adjustment

Checking the spark plug

The spark plug is an important engine
component, which is easy to check.
1
Since heat and deposits will cause any
spark plug to slowly erode, the spark
plug should be removed and checked
2
in accordance with the periodic mainte-
nance and lubrication chart. In addition,
the condition of the spark plug can re-
3
veal the condition of the engine.
To remove the spark plug
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1. Remove the spark plug cap.
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6
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1. Spark plug cap
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2. Remove the spark plug as shown,
with the spark plug wrench includ-
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ed in the owner's tool kit.
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11
12
1
1. Spark plug wrench
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To check the spark plug
1. Check that the porcelain insulator
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around the center electrode of the
1
EAU19605 spark plug is a medium-to-light tan
(the ideal color when the vehicle 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
erosion and excessive carbon or
other deposits, and replace it if
necessary.
Specified spark plug:
NGK/BPR6ES
3. Measure the spark plug gap with a
wire thickness gauge and, if nec-
essary, adjust the gap to specifica-
tion.
1. Spark plug gap
Spark plug gap:
0.7–0.8 mm (0.028–0.031 in)
To install the spark plug
1. Clean the surface of the spark plug
gasket and its mating surface, and
then wipe off any grime from the
spark plug threads.
2. Install the spark plug with the spark
6-8