Driving home from work this afternoon, out of the blue, my engine started
cutting out at highway speed only and only under light acceleration.  It's
an 83.5 H2O-cooled, fairly new, with great compression.  I got off the
freeway and took a lightly traveled surface road most of the way home.  Then
got back on the freeway for the last few miles; symptoms didn't recur.
Shouldn't be the fuel filter; it's fairly new.  Any clues?