You'll struggle to get a jet kit these days and you need the HRC emulsion tubes to go with the HRC needles.

But the needles are not your concern, they're just for fine tuning, it's the main jet that stands a good chance of being too small;

Stock NSR250 mc28 - 40bhp on the dot
Modded NSR250 mc28, HRC card, race pipes, maybe a couple of holes in the airbox - 60+ bhp

That is a huge amount, 50+% extra power and I don't know anybody who's run one without the full HRC jet kit.
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