This is normal. Without vsync, the only way to limit the framerate in a predictable way is to waste CPU time in empty loops.
I created code in my game to limit the frames rendered to 60 for cards that don't have vsync.
I wouldn't bother with this. vsync has been around for ages. Worst case scenario, you'll draw more frames than needed (probably not, though, since hardware that old would probably be fairly slow, anyway). At least the computer will be doing marginally useful work.