Fouling Plugs

What are they fouling with?
Oil?
Grey deposits?

Can you post a picture of one?

Cheap gas causes grey deposit buildup.
Don't have a camera with me but they basically look wet & a little carboned, as if it's running way rich. I'm running 98 fuel all the time. From what I have looked up the carb is supposed to be running size 72 jets from factory (Holley 3310-4). I have dropped the plug gap to 0.8mm on this set - havent pull them out to check how they are going yet.