Pics or it didn't happen, I'm hearing.
Pulled a frame down from the Atelier, this is an early 80's KHS touring frame with cantilevers. The cantilever bosses on the fork are typical for this era. I threw on a set of Tektra 720's to show how limited they are to open.
Here's the culprit:
Brake pads hit the fork blades, limiting how far they'll open. Note that the Tektra pads are on the short side for most modern cantilever brakes.
One solution is to use brakes with very short pads. Vintage MAFAC cantilevers work in this application:
Modern cantilever braze-on posts are made to braze on further apart, and stick out further from the fork.
The tiny Dia Compe brakes that came with many of these bikes (including this KHS) are on the low end in braking power, from my experience.
Moving the posts on this Expedition removes the one wart on it.