If you're running an NSR250 PGM-II*, I would strongly advise getting yourself an MC18 Mk2 flywheel, and a set of TA21A carbs at the very least.
However, personally, I would also recommend sourcing the R5/6K air correction parts too, because regardless of whether it's a track bike or not, it all just works so well! If you're willing to pay someone a few hundred quid for dyno setup time, then go for it, but you have to find someone who [a] knows how the PGM system works, so can work around it, and [b] someone who wants to then take that job on. I'm sure there are plenty of dyno shops that will say "yeah, bring it on in", but there are very few people, in my 25+ years of experience, that actually know what the NSR PGM system actually does.
PJ/PWK38s are a nice idea, but in my experience do not work as well on a 250... not even on a full TT-FIII setup, until the very last couple hundred RPM in the top couple of gears. The cost (particularly of the required manifolds) is rather significant, and the NSR250 loses everywhere apart from those last couple hundred RPM, where the 38/39s claw some back. They do seem to work much better on the 300s though, where the increased capacity seems to help draw on them better, and the induction roar from them is both epic, and I'm pretty sure worth another 5hp down the pub!
*Don't even get me started on NF5 and NH3 PGM-IIs! Please ensure you're using an NSR [KV3] PGM-II, else you'll be chasing your tail til the end of days! If Fontyyy was still active on the forum, I'm sure he'd happily corroborate!
The "standard" NSR250 carbs are designed to run with the air correction. The TT-FIII carbs are designed to run with the NH3 setup and no air correction, and while they look as good as identical, they differ internally to the stock carbs. It's why the RS PJ/PWKs can be set up more easily with no air correction, but they are just too big, and lose the bottom-end/mid-range over the 32mm carbs. I think, in an ideal world, the best NSRs would benefit from 34mm carbs, but the 32mm stockers are good for over 70hp anyway.
If you go for an unconventional setup, I wish you all the luck in the world, and hope you can get it sorted, but I honestly don't think it's worth the pain. The expense and time can be much better spent elsewhere.
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Andy.
NSR-WORLD.COM
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