It could be a lot of things. I'd check the basics first. If you think its bad gas run the tank down. At the next fill up add a bottle of Techron to the near empty tank and fill it up. Then drive as you normally do. You can also clean the carb, check the air, filter, cap wires, timing, etc. and check for vacuum leaks.
**Vacuum leaks can cause all kinds of problems, and might just be your problem.
When was the last time it was cleaned up? When was the last time the fuel filter and air cleaner were replaced?