I once tried an OS 7D carb on a ST 90 to see if it would clean up the rich and ragged mid-range. The result was little....if any improvement.

I was suprised at the results since others on here have claimed that replacing the stock ST carb with an OS carb made their ST 90s run perfectly. But that wasn't my experience.

I now suspect that the porting and timing of the ST 90 may have more to do with the mid-range problems than the stock ST carb.