The '28 is by far the hardest NSR to get power from;

The exhausts have restrictors in the headers (and weigh a ton), either replace the chambers (Tyga are good and cheap) or take the pipes off and spend some time with a dremel removing them.

Like all NSR's the airbox is restrictive, 4*1" holes in the lid seems to works best.

The ignition is retarded, a vaguely effective workaround is to use the flywheel from an MC21 but you're not going to get really good power (anything over 60bhp) out of a '28 on the standard card, the HRC card is the way forward.

As with all mods, check the jetting
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