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

Water Pump Impeller Disassembly/Assembly
Water Pump Housing DisassemblyCylinder Head Warp Inspection
Clean the cylinder head.
Lay a straightedge across the lower surface of the cylinder
head at several positions.
Use a thickness gauge [A] to measure the space between
the straightedge [B] and the head.
Cylinder Head Warp
Standard: – – –
Service Limit: 0.05 mm (0.0020 in.)
...
Brake Light Switches
When either the front or rear brake is
applied, the brake light goes on. The
front brake light switch requires no adjustment,
but the rear brake light switch
should be adjusted in accordance with
the Periodic Maintenance Chart.
Inspection
Turn the ignition key to “ON”.
The brake ligh ...
Shifting Gears
Close the throttle while pulling in the
clutch lever.
Shift into the next higher or lower
gear.
Open the throttle part way, while releasing
the clutch lever.
For smooth riding, each gear position
should cover the proper rate of speed
shown in the table.
WARNINGDownshifti ...