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 InspectionBalancer Assemble
Apply molybdenum disulfide oil solution to the ribs of the
balancer [A].
Apply molybdenum disulfide oil solution to the ribs of the
balancer gear [A].
Check that the rubber dampers [B] are in place.
Face the linked portion [C] to the bottom.
Assemble the balancer weight ...
ESD (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
...
Air Cleaner Housing Removal
Remove the fuel tank (see Fuel Tank Removal).
Disconnect the secondary fuel hose [A] from the delivery
pipe of the nozzle assy [B] (see Fuel Hose Replacement
in the Periodic Maintenance chapter).
Disconnect the secondary fuel injector connectors [C].
Free the lead from the grooves [D].
...