If you have power brakes make sure you don't have a leak around the brake booster.I had one that leaked once and it took me forever to find the problem.Pinch the vaccum hose off that goes to the booster and if the engine smooths out bingo.Mine was leaking at the seal where the brake master cyl bolts to the booster.If this isn't your problem check that you have the right source of vaccum going to your distributor advance.In most situations it should be ventura vaccum.......I think.........anyway it shouldn't pull any at idle but should as you rev the engine.I had mine hooked up wrong once and when I found the problem I had to reset my base idle and ignition timing.Good luck and if I can think of any more possibilities I will post them.
