If the surface is corroded or if the blades are damaged, replace the impeller

Water Pump Impeller Disassembly/Assembly
Water Pump Housing DisassemblyIdle Speed Inspection
Start the engine and warm it up thoroughly.
With the engine idling, turn the handlebar to both sides
[A].
If handlebar movement changes the idle speed, the
throttle cables may be improperly adjusted or incorrectly
routed, or damaged. Be sure to correct any of these
conditions before rid ...
Battery Ground
Before completing any service on the motorcycle, disconnect
the battery cables from the battery to prevent the engine
from accidentally turning over. Disconnect the ground
cable (–) first and then the positive (+). When completed
with the service, first connect the positive (+) cable to the
p ...
Stick Coil Primary Peak Voltage Inspection
NOTE
Be sure the battery is fully charged.
Remove the stick coils (see Stick Coil Removal).
Do not remove the spark plugs.
Connect the ECU to the harness.
Measure the primary peak voltage as follows.
Install the new spark plug [A] into each stick coil [B], and
ground them onto ...