Bill, there are a couple variations of cable assemblies, but in general, they all serve the same purpose. Yes, on each of our karts, we have a bare steel braided cable which is housed inside a sheath/sleeve (could be vinyl, plastic, teflon tubing – whatever). If the cable you use is coated in vinyl, I wouldn’t fret over using a bare steel cable. As Bo said, you might look at getting a whole assembly (cable and sleeve) – you will need to make sure that the anchor on the cable is what will fit your carb slide though.
We may not be the fastest on the track...but we're having the most fun!