engine not producing enough vacuum

Vacuum secondary carbs do not operate on engine vacuum. So the low vacuum reading your getting has nothing to do with the outboard card not working.

Hook you vacuum advance on the dist to manifold vacuum, that will help out a lot. Make sure you don't have really LIGHT advance springs either. You may have to use a limiter plate/advance spring kit to re-curve your dist.

Also you need to make sure the center carb is adjusted correctly. Its a pain but if its wrong it will run like crap.