I'm using Autolite 3924 plugs in my aluminum headed 454, Holley 780 carb, appx 10:1 compression. Yesterday, I put 2 new plugs in #1&2 cylinders, wound it out to about 60 mph for awhile, then coasted to a stop, shutting the engine off as soon as I could. Replaced those two new plugs with the ones I took out, then headed home. Back home, I cut the threaded base off one of the new plugs and found that the insulator was mostly white with a slightly tan band about 1/8" wide at the bottom. I was expecting to see some black so I could get an idea of where to go with a change in jets, but maybe more running time was needed to see that?
The jets that are in the primaries now are 72's any ideas where to go from here?