Breaking in a new GT-4. NGK B6HS. Smaller plug gap, .020-.025 had the top end clanging and rattling. Predetonation? Re-gapped to .030 to retard the timing, and most of metallic rattling has ceased but bike a little slower on run up. Using Shell 87 octane. Does higher octane affect these engines as far as predetonation goes?
Grubee instructions plug gap is .036?