Hi, just to set things straight, I know stuff all about these NSR carbies, though I have played around with PJ and PWK items for road racing. I also have a 2stroke carbie policy of, the bigger the better, and again, this is usually at odds with the established tuners... a matter of volume verses velocity in most cases. So I'll get on with my theory and why I'm asking for whatever advise you wish to give.

I ran a Honda CR250 many years ago and swapped the stock 34 for a 40 and got absolutely heaps of power, and have gone against convention with the 85 cc road racers I have run and replaced 28mm carbies with 34's and have always made good h.p.. My theory being that as atmospheric pressure PUSH's air into the crankcase, rather than the crankcase sucking it in, and the bigger the hole to let it in the quicker it gets filled. I know about the velocity principle, and it works well on 4 strokes, thou I believe that it has limited effect on forcing more mixture into a crankcase of a 2stroke due to the speed of the returning piston down stroke, so it"s get it in there while you can before the pressure shuts of the reeds. Anyway my theory, rubbish or not.

And to the point, I have a set of MC 28 carbs that I'd consider running on my 18/R5, and possibly having them machined out to a 34mm bore, as it seems a bit easier than welding up a manifold and finding a couple of PJ's at present, thou not out of the question. I see that the MC28 carbs have a much simplified air bleed system with one set of feeds and a weird solenoid setup, and really I'd like to do away with the bleeds, I have picked up that the F3 bike didn't use the bleeds, and neither do any of the RS series race bikes. Also you can set up a bike to run very well just using the right needle and main, etc.

Now I'm not looking at tooling about the daily commute on my bike, it's being prepared as a period production racer, so it does not need to be tractable across the rev range, just good when getting on the gas and wide open. So without any.. your a goose comments, does anyone have any experience with this, or is anybody able to possibly expand on the concept of not using the airbleeds. Cheers jeff.

Hummmmm, so no on has any advise, or possibly any experience with not running the air bleeds, I guess I'll have to just suck it and see for myself then.. Cheers.

And suck it, it was.... The dyno side of the our NSR program decided to find out what the real story was with the air bleeds in or out of operation, as I'd been going mad with not finding any info...... yeah, surely you guys with all the stars must have known this anyway and were keeping it quite... So an MC21 on the dyno with open carbs, big jets, tyga pipes and solenoids set up as factory. X.3 h.p.@ 12,500 rpm.
Same MC21 set up,same jets but with JHA chambers and the solenoids set up as factory.......X.0 h.p. and only 12,000rpm

I'm not telling what the real figure were but the story is pretty plain to see. The JHA's made a bit more mid range from 8,000 than the tyga's.

Off with the air bleeds and plug the lines... shite... and then with some normal main jets in the bleed lines, and after several runs from smaller to larger and then back again we have these figures to consider. Tyga piped MC21... X.3.3.h.p.@ 12.500 and the JHA's giving ...X.1.h.p. @12
So the carbs will run very well indeed without the air correction solenoids by placing a 140>150 main jet in their place. But the real surprise was the mid range gain from 8,000 rpm to 10,000 rpm where the JHA pipes made an extra 2 foot pounds of torque. This was also reflected in the Tyga pipe mid range, 1.8 flb and as the Phantom of the dyno said...made very angry motor.

Well that's it, the truth's now out there, whether you want to use this info, or whether it suits your riding environment, who know's but as racers it is really good news for us NSR production racers. Cheers Jeff