Sounds very much like the T.P.S., and very much like the symptoms Matt (TYGA) and I experienced on an MC28 motor fitted with RS250 carbs (no T.P.S. on the RS).

When an NSR sensor was fitted and turned to the correct setting, everything cleared up nicely!

Dave, PM me and I may be able to help you out with a set of carbs to "try".

Andy.
NSR-WORLD.COM