I got the best improvement from a CR8EIX Iridium plug. The standard plug, CR7 and its Iridium equivalent (CR7EIX) both made the bike feel lumpy, and I originally thought it was a problem with fake NGK plugs.

I think it may have to do with the power commander / stage 3 making the engine hotter? So a higher rated plug is required for me?

Not sure of the exact combustion science, but it works for me.

It'll only cost you a few quid to try it out.

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Bike: 2013 XT660Z, TKC70 tyres

Mods:
Barkbusters, Scottoiler, DIY Tail Mod, DNA Stage 3, Power Commander V & O2 Eliminator, Exan X-Black Stainless exhaust, Tool tube, Ohlins linear front fork springs, Nitron rear shock, JT front and Supersprox rear sprockets, D.I.D. VX 520 chain, Adventure Spec bashplate, DIY USB Outlet, DIY chain guide, Kev's Throttle mod

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