I think the needle needs to either be shortened a little bit or re-profiled to have a more gradual taper. I don't think it needs that much material removed, just enough to flow enough fuel at WOT and still idle and transition well. Pictures below show the GMS carb (brass spraybar) and a TT Pro carb (steel spraybar). I think I'd have good success if I chucked up the spraybar and shortened it a little bit and smoothed the end down some like the TT carb.