O.S. Engines 18TM Revo - Manual (Page 26)

CHECKING THE ENGINE
Engine will not develop normal performance
after long time running due to wearing of parts.
It is suggested to replace necessary parts when
the following symptoms are detected.
Engine sound changes and easily overheats.
Power has dropped extremely.
Idling is unstable and/or engine tends to stop
at idling.
In most cases, ball bearings, cylinder & piston
assembly, connecting rod and/or crankcase have
become worn out or abnormal. Check the
parts carefully and replace them if necessary.
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