This is probably a basic question, but was wondering if you guys might have some insight...

Plugs in the photo are laid out like they were in the motor...#1 on the bottom left, #8 on the upper right. From what I can tell I am running rich (no surprise) but what I don't understand is the four corner cylinders #1, 2, 7, 8 seem to be blacker than the four inside cylinders.

What would cause this difference? When I switch jets, how many sizes leaner should I go? Anything else I need to do?

Motor is a 440 with an 800 Demon, Wieand Action + two-plane intake, ported 906 heads, MSD, and soon to have headers replacing HP manifolds. Thanks!

i had a friend that had the 4 corner ones black and the rest ok. turned out that the rocker arm pole (cant remebmer what its called but the shaft that holds the rockers) was wearing down on the ends a bit. the slight lift it had in it wore the valve stem guides a bit and a little oil was seeping down there. we put in a new cam, rockers, rocker arms, lifters, and pushrods, and guides and its fine now. this could be the case with yours but may be something else. this is just my opinion dont take it to heart do some more research before you rip everything apart.