How did I miss this thread until now?
Lots of memories of these bikes - all the stuff that was dirt cheap in the 1980s: CT90/125, SL70/100/125, DT125, DT80, XL75/100, CL100 (or was it 90?), YG1, V90 step-through:D, etc.
I've got a TS90 in the shed, along with Doc's SL100, and my AT1 shitter and my AT2 project - but I really want a DT100 (one of the 'full-size' ones). Seems that everytime I find one, it's in triple-buggery, I'm broke or the Ebay seller is a cock-smoker...
There's also one of each of the three main incarnations of DT175s and the VMX-spec DT125A and CT1, but I think Tim's talking more about the smaller capacity, trail-bike trail-bikes.
Here's a pic of the AT1 when I bought it:
And this is the AT2 as it was a couple of months ago. Work has been embarassingly slow - it now has forks and a front wheel, and one rear shock...