Causes of unsteady idle/WTB heater control valve?

I think you were right the idle mixture was too lean, I turned the screws out bit by bit and it seemed to run smooth. I have a new big problem though; I just drove to another town about an hour away and I nailed the gas once on a back road. When I let off the gas and slowed down to turn the engine started to run really rough. I checked the ignition system and it seems to be OK, I feel like it's the carb because it only runs rough at low speed/just off idle; if you give it enough gas it accelerates smoothly with no misfiring. What should I look for?

EDIT: No vacuum leaks either I checked all that over