Rough idle could be a couple of different things. 1. Bad gas. 2. Dirty carb. 3. Coil going bad. 4. Sticking valves. You're going to have to do some troubleshooting to figure it out. I would start by changing the fuel and rebuilding the carb.
I usually start with the simple easy no brainer things like good fuel, good spk plgs, and a new air filter. A dirty air filter will change your air to fuel ratio to too rich almost like having the choke partially in the "on" position