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357 Posts
I am pretty Sparky :doorag: so I take a swing at it.
The stock plug that comes OEM with the bike is NGK CR8EK just as you said above.
The CR9EK plug will also work but it is a cooler heat range.

CR7EXI & CR8EXI are both iridium plugs.
The CR7EXI is hotter heat range plug than the CR8EXI
The lower the number the hotter the plug is, the higher the number the cooler the plug is.

Personally I would not run a hotter plug than the OEM heat range unless you had a specific reason to do so, such as you find the standard "8" heat range plug fouling due to an extremely rich AFR. Even then I would personally address the problem by tuning the AFR instead of going to a hotter plug. Going to a hotter plug can can cause pre-ignition problems if you are not careful. The heat range of the spark plugs used in our bikes was engineered for the bike by Suzuki already, there is really no reason to deviate from that. I have used a cooler heat range plug (9) in my M109's at times when the standard 8 heat range was not available. For all practical purposes the standard 8 heat range plug is what you want to run in your M109R, no matter if you run the OEM plug or you run iridium plugs.

Also I think you are running our ECU tune (I may be wrong about that though) our ECU tunes are built using NGK CR8EXI iridium spark plugs and running 93 octane pump gas.

I am planning to do Dyno this spring if all goes well but I have Cobra Fi2000 PowrPro Tuner Black I did see almost an instant change on the bike in the first 30 mins been happy with it so far... I'll be total honest while I try use USA gas only, I do not always run 93 honestly... I do have one local place sells non-ethanol 91 I sometimes run put in my '88 JD lawn mower LOL
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