Honda 2009 FSC600 Owner's Manual page 114

Use of lower octane gasoline can cause
persistent ''pinging'' or ''spark knock'' (a
loud rapping noise) which, if severe, can
lead to engine damage. Light pinging
experienced while operating under a heavy
load, such as climbing a hill, is no cause
for concern.
If pinging or spark knock occurs at a
steady engine speed under normal load,
change brands of gasoline. If pinging or
spark knock persists, consult your Honda
dealer.
Never use stale or contaminated gasoline
or an oil/gasoline mixture. Avoid getting
dirt, dust, or water in the fuel tank.
Servicing Your Honda
Fuel
105