I would check out the

www.type2.com
go to Type2
look in their mail.
More people here would running dual carbs and might be able to help with tuning tips.

and go to their archives and ask for help from A BUG/Bus/Vanagon Club in your area.  They would know a dual carb guru that could help you tune your carbs.

With my T4 engine and dual 40 Dells it goes in fourth gear from 35mph to 100+ mph (US MPH) and was getting @30 mpg.

Another place to go is the newsgroup:

rec.autos.makers.vw.aircooled

Look for related info or ask for help from someone in your area on tuning your carbs.  VW folks generally are real helpful folks.

Robert