Cleaning And Adjusting Spark Plug - Yamaha F9.9J Owner's Manual

Maintenance
EMU44490

Cleaning and adjusting spark plug

The spark plug is an important engine compo-
nent and is easy to inspect. The condition of
the spark plug can indicate something about
the condition of the engine. For example, if the
center electrode porcelain is very white, this
could indicate an intake air leak or carburetion
problem in that cylinder. Do not attempt to di-
agnose any problems yourself. Instead, take
the outboard motor to a Yamaha dealer. You
should periodically remove and inspect the
spark plug because heat and deposits will
cause the spark plug to slowly break down
and erode.
1. Remove the spark plug caps from the
spark plugs.
1
1. Spark plug cap
2. Remove the spark plug. If electrode ero-
sion becomes excessive, or if carbon and
other deposits are excessive, you should
replace the spark plug with another of the
correct type. WARNING! When remov-
ing or installing a spark plug, be care-
ful not to damage the insulator. A
damaged insulator could allow exter-
nal sparks, which could lead to explo-
sion or fire.
[EWM00561]
Standard spark plug:
BR6HS-10
64
3. Be sure to use the specified spark plug,
otherwise the engine may not operate
properly. Before fitting the spark plug,
measure the electrode gap with a wire
thickness gauge; replace it if out of spec-
ification.
1. Spark plug gap
2. Spark plug part number
3. Spark plug I.D. mark (NGK)
Spark plug gap:
0.9–1.0 mm (0.035–0.039 in)
4. When fitting the plug, wipe off any dirt
from the threads, and then screw it in to
the correct torque.
Spark plug torque:
ZMU07835
25 Nm (2.55 kgf-m, 18.4 ft-lb)
TIP:
If a torque-wrench is not available when you
are reinstalling a spark plug, a good estimate
of the correct torque is 1/12 turn past finger-
tight. When you are installing a new spark
plug, a good estimate of the correct torque is
1/2 to 2/3 turn past finger-tight.