Keep in mind that a GOOD folder which doesn't creak, groan and fight you in your quest for speed is a rare thing. I've ridden a Dahon folder and it's fine if you're going to toddle around a city as a tourist riding at a sedate pace. It's not a bike I'd want if I were riding for fitness or trying to get to work at a good turn of speed because I slept in a bit.

A good riding bike does not need to look expensive. There's many thousands of good quality CrMo framed bikes of yesteryear out there that will ride like the wind yet are rough enough looking and old enough in their components that they can sit locked up under a tree or other cover all day and no one will bother with them. It's just that with your Yorkville you got one of the heavier basic bikes.

What you want to look for in older bikes is the stickers on the frame that say what the material is. You're looking for the terms "Chrome Moly" or "CrMo" along with "butted" used in combination with words such as "special" or "double". These are indicators of the good quality higher performance older bikes. Be they an older mountain bike or 700c bike they signify that it's a bike worthy of careful examination of the rest of the drive train to see if it can be brought back to functional use for not too much money.