On my 1977 Centurion Pro Tour I have a Suntour Cyclone GT tied to a Suntour Barcon.

Sometimes in the low gears the chain will jump to the inside of the guide pulley, lodging against the cage of the derailleur, usually pulling the chain between the freewheel and the spokes. The teeth on the pulley look slightly worn, but not overly so.

Does anyone have any insights into what might cause this? It happened twice when I first got the bike a year ago, and then three times yesterday on my way to work. Then I got a puncture at midnight on my way home...

I'm thinking about disassembling, cleaning and lubing all the pivots again to make sure the springs are snapping it back into place quickly.