Yamaha F5A - Checking the Spark Plug; Checking the Thermostat; Checking the Thermostat Cover Anode

7-35
POWR
Power unit
• If the valve seat contact area is too narrow
and situated near the bottom edge of the
valve face, cut the bottom edge of the valve
seat using a 60° cutter to center the area,
and then set its width using a 45° cutter.
b Previous contact width
7. After refacing the contact width of the
valve seat to specification, apply a thin,
even layer of lapping compound onto the
valve seat, and then lap the valve using
the special service tool a. NOTICE: Do
not get the lapping compound on the
valve stem and valve guide.
8. Recheck the valve seat contact area of
the valve. See “Checking the valve seat”
(7-32).
Checking the spark plug
1. Clean the electrodes a using a spark
plug cleaner.
2. Check the spark plug. Replace if the
electrodes are eroded, there is carbon or
other deposits.
3. Check the spark plug gap b. Replace if
out of specification.
Checking the thermostat cover
anode
1. Check the anode. Replace if eroded.
Clean if there is grease, oil, or scales.
NOTICE: Do not apply grease, oil, or
paint to the anode.
Checking the thermostat
1. Suspend the thermostat in a container of
water.
2. Place a thermometer in the water and
slowly heat the water.
Valve lapper a: 90890-04101
60˚
b
a
Specified spark plug: CR6HSB (NGK)
Spark plug gap b:
0.6–0.7 mm (0.024–0.028 in)
a
b