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Agreed, it is strange to see a 10 come stock in a 125. Sort of like a KX65 having a 10, but nearly everyone uses a 9, just to name one similar example of several. In the brave new world of computerized 2-strokes, i was a bit concerned about straying away from any stock settings or specs, but the 9...

Thanks for the reply and the piston picture! At least that is an easy location to check with the bore scope. I agree with you about cast versus forged pistons, and the nearly unobtainable billet machined (edit to: hardest to find) being the ultimate, but it is disappointing that the OEM cast piston isn't a safe bet in this case...

Jbone, thank you for all the effort you've put into this thread and the video series about this bike! Before i ask my question, i want to offer what we've learned so far: I bought my son a '23 KTM 125 XC last month. He has 11 hours on it now. The plug fouled at 2 hours. After switching to...