Thanks very much Raiyn and Retro Grouch. I will give your ideas a try. I don't think it is related to the tautness of the cable, however, as I have pulled it as tight as I can. Grouch, when you say barrel adjuster, you mean the one up by the handle, right? It is broken. One of my main problems is that I can't make adjustments with it because of the damned slit that gets caught on the cable.
Expatriate: Actually, because of the weak brakes, which have been a problem since I got the thing in '97, I have been too discouraged to use it much. It's very comfortable (with the marine seat) and easy to ride (with 36 gears) on any terrain, but it's difficult to ride at high speeds because of the instability.