Sounds like several possibilities:
Vacuum leaks around the intake manifold at the heads are common from loose bolts. A 13mm socket wrench is needed. Turn only 1/10 on each nut at a time. Don't overtighten. To get the nuts tight on the passenger side, you may need to remove the MPS mounting bolts.
Try to use some starter fluid with the engine running. The engine wil rev-up if a leak sucks the starter fluid into the engine.
You could have bad fuel pressure or injectors and it is not firing all jugs evenly. Check your fuel pressure with the engine running. I got my fuel pressure gauge from Sears (cheaper than mail-order since no freight) and I used a steel air valve (used from the Pep-Boys service dept) as the screw-on end connector. Hook the fuel pressure gauge up to the cold-start injector hose.
It could be a bad MPS with a leak in it. Check out
http://members.rennlist.com/pbanders/djetparts.htm and all of the related pages for more information.
Ignition is possibly the problem if the points are pitted. Small arcs can occur that will alter the performance of the ignition. Make sure that the little ground strap on the advance mechanism is solid and not frayed.
Good luck.
Joe