vac or mechanical secs?
bogs down & loses all power = lean
bogs down and slowy picks up then its fine = rich
i also had a problem of it would lose all power at 3000rpm +
turned out the coil was shorting out to the postive terminal
edit http://www.vw-resource.com/jets.html
have a GOOD read through that, explains how everything works and how to work out the basic tuning/diagnostic