expect this has been asked before but couldn't find out using the search option....when you increase the main jet size should you increase the the setting on the air screw?
i ask as i've put in larger mains to match the air box mod and wire splice and the bike runs great at half and full throttle but is a bag of shite at 1/4 throttle. at the moment the air screw is set at standard 2 1/8 turns out from fully in.
any ideas??

People on here are very cautious about giving advice, because every bike, and environment can be different. The tuning section on here -> http://www.nsr-world.com/tuning/250-tuning/carburation%20index/jetting/ gives a fairly good account of the NSR specifics, and when matched with this article -> http://justkdx.dirtrider.net/printcarbtuning.html although based on another manufacturer I think you will be able to work it out. Especially the quarter throttle tuning section. Cheers.

cheers had read the one on this site.... just wondered if using a larger main would leave a larger gap on the straight part of the needle when the throttle is shut, thus leting fuel through on small throttle openings?
gonna have another fiddle withe th air screw see if i can improve it.

When you say bag of shite, what are the symptoms ?

My MC21 was doggy off idle and the first 1/4 throttle. Bit smokey and fluttery when you go to take off. Felt too rich.
The air screws were set at 1-1/2 and 1-3/4 with factory jets. I changed them to 2 full turns out and it was definatly crisper, and alot easier to take off.

Mine has the same mods as yours. Air box, PGM and GPS splice and different mufflers. Std jetting tho
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sorted, float height was out should be 13mm but was 12mm.doesn't seem to take much to up set it ! lol. was making it run rich on 1/4 throttle.