AVS2 carb tuning. Anyone with experience out there?

I've got the same 650 AVS2 with a similar setup. 71 340, stock cam, Air Gap, 2500 stall, 3.55 gears. I haven't tried to tune it because the combo will be changing soon, but I get the same lean stumble if I'm too aggressive in the lower end. Goes like a raped ape after that. Runs really nice. Plugs look good, on the lean side. Just pulled the motor out this weekend and the base of the carb and the intake runners are clean as new. No soot whatsoever. I'm not going to be any help, but am looking forward to how you proceed.