Honda CRF50F 2017 Owner's Manual page 39

Use unleaded or low-lead petrol with a
research octane number of 91 or higher. We
recommend that you use unleaded petrol
because it produces fewer engine and spark
plug deposits and extends the life of
exhaust system components.
28
NOTICE
If ''spark knock'' or ''pinking'' occurs at a
steady engine speed under normal load,
change brands of petrol. If spark knock or
pinking persists, consult your dealer.
Failure to do so is considered misuse, and
damage caused by misuse is not covered by
Honda's Limited Warranty.
Occasionally you may experience light
spark knock while operating under heavy
loads. This is no cause for concern, it simply
means your engine is operating efficiently.