V91 is reportedly open chamber. It comes from Series 2 Bluebird.


> It doesn't matter if you are holding the throttle steady in this [RPM] range or accelerating

If the 1500-3000 RPM roughness occurs when NOT accelerating -- just holding the speed steady -- and the throttle is open a ways, then it is caused by the main jetting. This is the combination of Main Jets + Air Correction jets. With throat size 30mm, use Main Jet 120 and Air Correction Jet 165 or 170.

But if at a steady speed, the thottle is barely open, then it is probably a transition issue. After adjusting idle speed to 800 RPM and mixture for Best Lean Idle, how far out is the Mixture screw turned? For the DCOE if it isn't near one turn the the Idle Jet needs to be changed. Likely the DCOM is the same.