You can use a needle tip attachment on the vacuum hose or wand.
It isn`t really a needle, just a pointed tip attachment that can help cleaning in tight areas like the pistonto cylinder wall area.
Try to not use a scraper on the carbon, it doesn`t do nice things to the top of a piston if you gouge it while trying to remove the carbon. use some ATF (auto tranny fluid) to soften it up. Let it soak,

There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us.
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Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!