Could be a number of things.
I'd check the following:
1) Clean the carb. Might be flooding out. You can check this by popping off the air filter and simply smelling. If it reeks of gas then you might need a clean/rebuild.
2) Check for vacuum leaks. Start by pinching vacuum hoses. Then move on to spraying around the carb with carb cleaner. If it runs smoother during any of these you'll likely pinpoint your problem.
3) Check timing. 8-12 degrees advanced depending on the engine.
4) Might be a bad cam. Does it run rough at idle after all the above? Pop the valve cover off and look for broken valve springs. As a last ditch you can remove the plugs and hand crank the engine while measuring the lift with a fine ruler. When my cam went the car did the same as you're describing. As I said, though, last ditch effort here.
I suspect either a vacuum leak or timing. Could easily be a gummed up carb if you haven't run it in a long time.
