Honda Harmony HRM215SXA Owner's Manual page 57

MAINTENANCE
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 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.
1 NOTICE 1
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.
For
oxygenated fuel information refer to page 91,
55