Slide out the rubber cap [A].

Starter Motor InstallationTachometer
The tachometer shows the engine
speed in revolutions per minute (r/min,
rpm).
On the right side of the tachometer
face is a portion called the “red zone”.
Engine r/min (rpm) in the red zone is
above maximum recommended engine
speed and is also above the range for
good performance.
...
Clutch Plate, Wear, Damage Inspection
Visually inspect the friction and steel plates for signs of
seizure, overheating (discoloration), or uneven wear.
Measure the thickness of each friction plate [A] at several
points.
If any plates show signs of damage, or if they have worn
past the service limit, replace them with new on ...
Balance Inspection
Remove the front and rear wheels (see Front/Rear Wheel
Removal).
Support the wheel so that it can be spun freely.
Spin the wheel lightly, and mark [A] the wheel at the top
when the wheel stops.
Repeat this procedure several times. If the wheel stops
of its own accord in various positi ...