They appear to be a cross between carbon-fouled and ash fouled.
Jerry S.
I'd check the air cleaner (probably change it if I hadn't in awhile
just because), and change the plugs and wires.
Then I'd check the plugs in a few thousand miles... new plugs and
wires can work wonders in the short term for hiding a symptom.
Good luck Jerry!
Rob
becida AT comcast.net
Western Washington State, USA