Honda FR650 Owner's Manual page 15

Fuel Recommendations
Use unleaded gasoline with a pump octane rating of 86 or higher.
This engine is certified to operate on unleaded gasoline. Unleaded gasoline
produces fewer engine and spark plug deposits and extends exhaust system
life.
Never use stale or contaminated gasoline or an oil/gasoline mixture. Avoid
getting dirt or water in the fuel tank.
Occasionally you may hear a light "spark knock" or "pinging" (metallic rapping
noise) while operating under heavy loads. This is no cause for concern.
If spark knock or pinging occurs at a steady engine speed, under normal load,
change brands of gasoline. If spark knock or pinging persists, see an
authorized Honda servicing dealer.
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Running the engine with persistent spark knock or pinging can cause
engine damage.
Running the engine with persistent spark knock or pinging is misuse, and the
Distributor's Limited Warranty does not cover parts damaged by misuse.
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