If you search, there is a thread on the Evo 100 & 46 and how to tune them correctly. It seems many have the collars installed incorrectly at the factory. The low end needle should start at 1 1/5 turns out.

Another thread mentions about adding a stronger spring inside the carb to stop the rotating barrel from vibrating in and out.

There was a thread just recently about how bad the ST 90 carb was.