piston heads

1997 Yamaha 130. Took the heads off to clear the water passages to try to cure an overheat problem. Pistons show carbon on top. Should I remove it and if so what is the best way to clean them? Or do I put it back together and do a decarb?

Scout 185

clean it while its apart, use a foaming decarb cleaner
then do a decarb

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