Here are some pics for those that have not seen what a "carb" pipe looks like.
Firsy, the Aerosphere and the Kaywoodie side by side. The Aerosphere, I bought from Cyndi. It came in very good shape, with only very minor wear. The Kaywoodie, I bought off Ebay, and it was screwed up. The stem was overclocked (screw in type stinger) and the carb hole was plugged, (possibly intentionally). I rehabbed the Kaywoodie by re-clocking the stinger, and boring out the carb.
Next is the carb hole on the Aerosphere. It is in the stem, and consists of a brass fitting / plug with a small hole. It introduces air when you draw on the pipe, making for a cooler smoke. It actually works very well, and doesn't over-draft, even while lighting. The pipe smokes well, and you can always put your finger tip over the hole while drawing if you just want to introduce less draft for some reason.
And, finally, the carb on the Kaywoodie, which is located on the bottom of the bowl. It is also a brass fitting, with the same function as described above. It works well, and as described, although I tend to cover it with my finger when I light the pipe.
So, there you go....