I refrained from posting when I first saw this post this morning, but I suspected a too lean condition. I read the thread listed in the above post and indeed, there are a few lean condition theorists, too.
You didn't mention if you had tried a little richer GAV setting...a little more open, in other words. You might try opening the GAV about another 1/4 turn and see if that addresses your issue. If not, then I'd suspect an air leak somewhere around the carb-to-manifold joint, or around the manifold gasket...both of these will cause a lean condition. If you suspect that...with the engine warmed and idling, try squirting some WD40 around the joints between the carb/manifold and manifold/head. If you get any change in your idle speed...then there's your leak. If no change in idle, then it's something else.
Hope this helps...let us know what you find...
