The RC51 responds to spark plug changes more so than any other bike I have owned.
We have actually seen 1-2 hp gains from simply installing new plugs at 4000 mile intervals.
& the increased throttle response can be detected even without a dyno.

It is also important to know that you cannot gap the plugs on the RC due to the
high probability of damaging the delicate iridium electrode

PART #'s
FR9BI-11 (00-01 NGK)
IK27C11 (00-01 NIPPON DENSO)
IFR9H11 (02-03 NGK) 31919-MEB-671
IK27PRZ11 (02-03 NIPPON DENSO) 31919-MEB-672