Does it run well with the vacuum advance disconnected? If not, get that figured out first, and then and only then work on the advance.

And like shorty said, adjusting the screw only changes how much vacuum causes it engage. You'd have to take the cap off and find a way to limit/lengthen the travel to change how much advance it provides.

Ideally this is done with something like a mity-vac so you can apply measured vacuum at idle and see the 'curve', then adjust it accordingly.