I agree with doctorshoc. He sounds like he's got a good bit of knowledge. I'm guessing from your setup, that's what's happening. The one point I will argue him on is that spark plugs could cause a rich like condition. If the plugs are carboned up, they will make the engine miss and act like it's running rich because it's not burning the fuel completely. New plugs could help this condition. Also, make sure your plugs are the right heat range. If they are too cold of a plug, they will foul easily, if they are too hot, they will burn up. You may want to stick the recommeded stock plug size in to see if it makes a difference.

As far as fuel goes. I don't see any reason you can't run regular. What octane is it? I wouldn't go less than 87 octane on your car.