I've got these black rings around the insulators on all 8 of my plugs. Looks like carbon soot but it's actually burnt into the insulator. Very visible between the plug boot and the head.

What causes this? Too hot or too cold of a plug? Is this bad? How do I cure it?

Ignition system consists of an Accel 300+ digital race ignition and coil, MSD 8.5 wires and Accel 786 U-groove plugs.

Any ideas?

Thanks,
FLY

 

Old plugs. Over time they naturally get hot, and thus cook every little bit of dirt and funk that hits them into the porcelain. I don't think it's bad as long as your boots seal well. I suppose it could form a conductive coating that could casue it to miss if the boot didn't seal, depending on the composition of funk baked in. Carbon is a conductor.
...ed

 

The plugs have less than 3000 miles on them....?
Sorry, forgot to mention that.

FLY