How to adjust Ives Rota Closer
Odds seem excellent that it was  coiled spring closer, and the spring (having been overstressed by wide opening, and/or simply from old age) is now snapped, so "adjusting it" won't happen. Replace, with any suitable door closer (ie, it need not be this particular type, if it's hard to find, which seems likely)

Here's some info, though it does not directly confirm or deny my suspicions: http://www.epivots.com/mpowr-mp-800.aspx