Yamaha 90D, Owner'S Manual

Page: 49 / 77

Maintenance
44
EMU28951
Cleaning and adjusting spark plug
WARNING
EWM00560
When removing or installing a spark plug,
be careful not to damage the insulator. A
damaged insulator could allow external
sparks, which could lead to explosion or
fire.
The spark plug is an important engine com-
ponent and is easy to inspect. The condition
of the spark plug can indicate something
about the condition of the engine. For exam-
ple, 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 diagnose any problems yourself.
Instead, take the outboard motor to a
Yamaha dealer. You should periodically re-
move and inspect the spark plug because
heat and deposits will cause the spark plug
to slowly break down and erode. If electrode
erosion becomes excessive, or if carbon and
other deposits are excessive, you should re-
place the spark plug with another of the cor-
rect type.
Before fitting the spark plug, measure the
electrode gap with a wire thickness gauge;
adjust the gap to specification if necessary.
When fitting the plug, always clean the gas-
ket surface and use a new gasket. Wipe off
any dirt from the threads and screw in the
spark plug to the correct torque.
NOTE:
If a torque-wrench is not available when you
are fitting a spark plug, a good estimate of
the correct torque is 1/4 to 1/2 a turn past fin-
ger-tight. Have the spark plug adjusted to the
correct torque as soon as possible with a
torque-wrench.
EMU28962
Checking fuel system
WARNING
EWM00060
Gasoline and its vapors are highly flam-
mable and explosive. Keep away from
sparks, cigarettes, flames, or other
Standard spark plug:
B8HS-10
BR8HS-10
1. Spark plug gap
2. Spark plug I.D. mark (NGK)
Spark plug gap:
0.9–1.0 mm (0.035–0.039 in)
Spark plug torque:
25.0 Nm (18.4 ft-lb) (2.55 kgf-m)