I don't have experience with the NS250, but what you are asking worked perfectly on my little MBX125F years ago.

It was like riding a TZR125 with the power valve turned wide open - very little bottom end until 7000rpm, then off it flew!

All the race pipes for the NS250 and 400 remove the ATAC, so I say go for it... and let us know how you get on!!
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Andy.
NSR-WORLD.COM

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