Being inconsistant like it is the first thing I would do is check the point gap. If it is to close where the points are barely breaking it can cause this. Check the gap with the rubbing block on top of a lobe. Then like Tommy says look for a vacuum leak. If the gasket between the manifolds is leaking it will not cause a vacuum leak though. It is stricktly exhaust. Tighten the bolts that hold the manifolds to the engine. There are 2 different geaskets that go between the throttle body & fuel bowl. Both come in the kit. It the wrong one is put in or put in backwards it can cause this kind of problem. I would try moveing the dist back & forth till it runs the best. You can make the final timing settings after you get it to run. If that doesn't do it take the carb off & go into it. They are not that hard to work on. What about the gas. Is it real old or have water in it.
