Have you fixed the "t" joint? At this point, changing jetting isn't going to do you any good until you get that part replaced.

Also, there is a Jha setup manual for a modified NSR. Would be a good starting point. But as always, specific jetting recommendations is nearly impossible to provide on an internet forum without risk. There are plenty of "guides" on what jets do what, who to tune a 2-stroke based on conditions, setup, etc.. Andy pointed to the jetting chart that addresses what each jet does what. Look for the Jha setup manual to see what they recommend based on their setup.

HRC has some good publications for jetting on an RS250 (jetting is jetting for the most part, so that guide will help you with what to look for and what to do for your specific needs).