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

Water Pump Impeller Disassembly/Assembly
Water Pump Housing DisassemblyOil Level Inspection
If the oil has just been changed, start
the engine and run it for severalminutes
at idle speed. This fills the oil
filter with oil. Stop the engine, then
wait several minutes until the oil settles.
NOTICE
Racing the engine before the oil
reaches every part can cause engine
seizure.
...
Valve Clearance
Valve and valve seat wear decreases
valve clearance, upsetting valve timing.
NOTICE
If valve clearance is left unadjusted,
wear will eventually
cause the valves to remain
partly open; which lowers performance,
burns the valves and
valve seats, and may cause serious
engine damage.
Valve cle ...
Ignition System
WARNINGThe ignition system produces extremely
high voltage.
Do not touch the spark plug, ignition coil or ignition
coil lead while the engine is running, or you
could receive a severe electrical shock.
NOTICE
Do not disconnect the battery cables or any other
electrical ...