There are quite a few things that can cause high hovering idle:
"1) The carb butterflys must both be able to freely close all the way. Synchronizing the carbs is part of doing this.................use a manometer (make your own)."
^^^^ I'm having this same issue, starts, idles fine, even in first gear it revs to 4k rpm and stays there constant after holding in the clutch but runs fine when going, literally just happns when i'm holding in the clutch. I know I don't have the butterflys "all the way closed" but i can see a tiny bit of light still, is it supposed to be 100% closed or maybe like 95%? I still have to check a couple others you listed for this issue.