Your plugs are probably carboned up like that from being too far advanced with the timing. When I advanced the timing on my GTX from its stock initial location at 6 degrees to 15 you could see the black smoke start to pour out of the pipes. Try putting it to stock for a while and it will probably clean the plugs up pretty good. Pull them after its run for a while and if they look good you should be good to go. It might be hard to burn all of the carbon off though.
Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street
