Setting point gap -- help!

This may sound dumb, but I notice that when I turn the elliptical adjusting screw to set the point gap, the whole point set will sometimes move. When that happens, a spring near the vacuum advance pops the lever up. When that lever is in the down position, I get no spark through the distributor, but I can't seem to get the dwell angle or the gap right when the lever is down. My shop manual is mum on this. What's happening??