Funny, nobody has mentioned my favorite way of removing carbon yet. When I first got my '91 it had about 230k on it, and ran like crap due to a number of things, including carbon buildup. I tried using seafoam, but after a whole bottle it only marginally improved how the engine ran. After a bit of digging around looking for something that would do a better job than seafoam I stumbled onto something that should have been obvious: water does a great job cleaning carbon.
Anyone who's had to replace a blown headgasket that's caused coolant consumption can tell you that the easiest way to spot where the gasket blew is to look for the cleanest combustion chamber. So I grabbed a small plastic soda bottle, punched a small hole in the cap, filled it up with water, and went out to the Jeep. I pulled the brake booster line off, started it up, and trickled water down the brake booster line. Now I knew I needed to be careful here, as dumping a large quantity of water into the intake would be a VERY bad idea. It would be more than a little embarassing explaining to the mechanic exactly how I managed to hydrolock the motor in my driveway. However, after emptying the bottle into the intake over the course of a couple minutes, I shut it off, hooked the brake booster back up (don't forget this! I almost trashed my neighbor's yard once after forgetting this), and started the Jeep up. Before I had done all this sitting in the Jeep at idle felt like sitting in some twisted amusement park ride, but now it was idleing smoother than it ever had for me. I went for a drive to the gas station, filled it up with regular (I had been using premium before), and it was still running better than it had in a long time. It's been about 10k miles since I did this and it's still running great on regular.
