spark plugs replace YAMAHA NIKEN 2018 Owners Manual

Periodic maintenance an d a djustment
6-10
6
EAU19653
Checkin g the spark plu gsThe 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.
TIPIf 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 plu
g cap, otherwise
the i gnition coil coupler may get
d amag ed . The spark plu g cap may
b e difficult to remove because the
ru bber seal on the en d of the cap fits
ti g htly. To remove the spark plu g
cap, simply twist it back an d forth
while pullin g it out; to install it, twist
it back an d forth while pushin g it in.
Specifie d spark plu g:
NGK/MR9K91. Spark plug gapSpark plu g g ap:
0.8–0.9 mm (0.031–0.035 in)
Ti ghtenin g torque:
Spark plug: 13 N·m (1.3 kgf·m, 9.6 lb·ft)
UBD5E0E0.book Page 10 Wednesday, April 25, 2018 2:23 PM

Periodic maintenance an d a djustment
6-35
6
EAU42505
Trou bleshootin g chartsStartin g prob lems or poor en gine performance
Check the fuel level in
the fuel tank.1. Fuel
There is enough fuel.
There is no fuel.
Check the battery.
Supply fuel.
The engine does not start.
Check the battery.
Remove the spark plugs
and check the electrodes.3. Ignition
Wipe off with a dry cloth and correct the
spark plug gaps, or replace the spark plugs.
Have a Yamaha dealer check the vehicle.
Operate the electric starter.4. Compression
There is compression.
There is no compression.
The engine does not start.
Have a Yamaha dealer check the vehicle.Have a Yamaha dealer check the vehicle.
The engine does not start.
Check the compression.
Operate the electric starter.2. Battery
The engine turns over
quickly.
The engine turns over
slowly.
The engine does not start.
Check the ignition.
The battery is good.Check the battery lead connections,
and have a Yamaha dealer charge
the battery if necessary.
DryWet
Operate the electric starter.
UBD5E0E0.book Page 35 Wednesday, April 25, 2018 2:23 PM