I found the iridium plug CR7EIX to be detrimental to the bike's performance.

It got horrifically choppy, and felt like unusual chain slack... engine pinking and basically struggling the whole time.

I have all the same mods as you.

Swapped to an iridium CR8EIX and the performance is better than ever.

Try this instead, or try a standard CR8E

Now the engine runs a bit hotter, thanks to the mods, a higher range plug seems to be the way to fix the problem you're having.

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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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