Hi javipop, i have RS125 and RS250 with drilled pistons, from the factory, these are full on race bikes, i also have modified mc21 i use for track days as well, no holes in pistons, and no problems with pistons overheating. I personally think it is not neccesary on standard NSR. Regards Les.
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Proud Father of , 05 ktm 400exc supermoto 2018 honda crf rx supermoto