Periodic maintenance and adjustment
6-8
6
EAU19653
Checking the spark plugs
The spark plugs are important engine
components, which should be
checked periodically, preferably by a
Yamaha dealer. Since heat and depos-
its will cause any spark plug to slowly
erode, they should be removed and
checked in accordance with the peri-
odic maintenance and lubrication
chart. In addition, the condition of the
spark plugs can reveal the condition of
the engine.
The porcelain insulator around the
center electrode of each spark plug
should be a medium-to-light tan (the
ideal color when the vehicle is ridden
normally), and all spark plugs installed
in the engine should have the same
color. If any spark plug shows a dis-
tinctly different color, the engine could
be operating improperly. Do not at-
tempt to diagnose such problems
yourself. Instead, have a Yamaha deal-
er check the vehicle.
If a spark plug shows signs of elec-
trode erosion and excessive carbon or
other deposits, it should be replaced.
Before installing a spark plug, the
spark plug gap should be measured
with a wire thickness gauge and, if
necessary, adjusted to specification.
Clean the surface of the spark plug
gasket and its mating surface, and
then wipe off any grime from the spark
plug threads.
TIP
If a torque wrench is not available
when installing a spark plug, a good
estimate of the correct torque is 1/4–
1/2 turn past finger tight. However, the
spark plug should be tightened to the
specified torque as soon as possible.
NOTICE
ECA10841
Do not use any tools to remove or in-
stall the spark plug cap, otherwise
the ignition coil coupler may get
damaged. The spark plug cap may
be difficult to remove because the
rubber seal on the end of the cap fits
tightly. To remove the spark plug
cap, simply twist it back and forth
while pulling it out; to install it, twist
it back and forth while pushing it in.
Specified spark plug:
NGK/LMAR8A-9
1. Spark plug gap
Spark plug gap:
0.8–0.9 mm (0.031–0.035 in)
Tightening torque:
Spark plug:
13 N·m (1.3 kgf·m, 9.6 lb·ft)
Summary of Contents for MTN690-U 2019
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