[700rpm]

If you have no way to measure the flow in your carb jets, then I would second Mitch's suggestion on obtaining jets from Renner's. In my recent experience of flow testing 30 original and new jets, I found only three complete sets that were just barely close enough to specs to use. Your problem lies in your jet size or your GAV adjustment; the air adjustment screw only affects idle, and works in conjunction with the idle jet and the secondary well. It is part of the idle system, and shouldn't impact how rich the engine runs at driving speeds. That is controlled with the GAV, as noted above by others.