After removing my headers on a 1976 460, the inside of the header tubes were black and sooty (rich condition) on the front four cylinders, 1,2, 5 and 6 and the rear four cylinders, 3, 4, 7 an 8 were clean (lean condition), 8 was only slightly sooty. The Holley 750 DP was rebuilt over the winter. Manifold is standard ford. I haven't found any air leaking into the rear of the manifold to make a lean condition. Any suggestions on what could be the cause? I want to richen the rear four cylinders.