The best way to tell is to drive it good and hard and see how the plugs
look then. It may be that it is only rich at idle. You have two sources
of black stuff, gasoline and oil. Oil makes them black and oily.
Gasoline makes them black and sooty/fluffy. Correct mixture makes the
plugs light tan and too lean makes them white.

But the terse answer to your question is, in the mode in which you
have been operating it, yes. Take it out and (like the song says)
drive it like you hate it.
--
George Downs Bartlesville, Oklahoma