On my 99 model I sent a flywheel, had a spare engine, to Steahly. Now that I've thought about it, they put 14oz on it. At the time I thought that would be TOO much but it made the bike much easier to ride and to start in awkward situations. Still had plenty of hit but didn't stall and idled much better too. The cost was a little high but worth it. $130 I wish I had done it when I first got the bike.
The rotax has right-hand threads in the flywheel puller hole, thats where the quick attach one's go, and they don't have that type (right-hand thread)available. They (Steahly)put a weight on your flywheel and machine it to suit.