my guess is, once you fatten up that needle, your main will require leaner ?
have you searched thru the 28mm jetting threads for a starting point ?....
http://www.blasterforum.com/searchresults.php?cx=partner-pub-9438014176008015%3A9127094460&cof=FORID%3A9&q=28mm+jetting&sa=Go
or....
http://www.blasterforum.com/carburetor-138/what-jets-you-using-28981/
i have been all over and its hard to find what ppl are using on a 28mm.... but the few i found was around where im at between 45-48 pilot and 155-165 mains.