I race an NSR250 and if you are not expecting the max power from it then you can tune it to be quite low-maintenance, whereas the RS250 will require more work. I know of an RS250 a friend here in Japan is selling right now. It comes with boxes of spares, heads ground to different heights, pistons, and the stuff you'll need to run it for a while etc. etc.. I can put you in touch if you like.
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MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
