If any is worn down to the service limit, replace the brush assy.
Starter Motor Brush Length [B] Standard: 12.05 mm (0.4744 in.) Service Limit: 6.55 mm (0.258 in.)

Starter Motor Assembly
Commutator Cleaning and InspectionESD (Electronic Steering Damper) ECU Error (Service Code E3b, ZX1000JD/KD)
If this service code appears, check that the following parts
are correctly.
Crankshaft Sensor
Gear Position Switch
Starter Lockout Switch
Main Throttle Sensor
Rear Wheel Rotation Sensor
If these parts are normal, check the ESD ECU for its
ground and power supply (see ESD ECU Power Supply
...
Stopping the Motorcycle in an Emergency
Your Kawasaki Motorcycle has been
designed and manufactured to provide
you optimum safety and convenience.
However, in order to fully benefit
from Kawasaki’s safety engineering
and craftsmanship, it is essential that
you, the owner and operator, properly
maintain your motorcycle and becom ...
Air Cleaner
A clogged air cleaner restricts the engine’s
air intake, increasing fuel consumption,
reducing engine power, and
causing spark plug fouling.
This motorcycle’s air cleaner element
consists of a wet paper filter, which cannot
be cleaned.
The air cleaner element must be replaced
in acco ...