Actually, carbon is an easy fix! If you can get to the throttle body, or whatever it has and pour something in it. Take a pop bottle and fill it half with trany fluid and half with warm water, shake it up and pour it in while it's running. You will have to kick the throttle up now and again, and it will smoke to high heaven, but it will burn it out!
There's also a lot of good fuel additives out there now that you might try. But if it hasn't had a proper tune up in a while, I'd hedge my bet towards that first, plugs wire, cap rotor and have the timing set. Not sure if that one has the stupid two piece dist cap or not, but those things are junk! If you can, try and find a single piece one to replace it with.