Finally, the midrange can be adjusted by rotating the spraybar a hair. Just loosen the two screws next to the high-speed needle and rotate the spraybar just a tiny bit. Either direction is OK. This will help you get a good transition and midrange.

From the SuperTigre MFG Support Forum http://www.supertigre.com/faq/product-faq.html#q22

The straight down the middle setting is the starting point like all other recommended carb settings.