I have pulled my 350 to do the oiling system mods I should have done when I last rebuilt it, and to do a little more aggressive porting to the heads. It has been running fine with the Comp 268 cam to this point. Look at the pic. These are the exhaust valves from the disassembled heads. They are positioned as if you are looking at the motor from the FRONT. Notice the progression of color from the front of the motor to the rear. Dark = front, Whitest = rear. I am assuming that the cause is it is A/F related, but I cant really make sense of the front-to-back color fade pattern. Who has a good explanation for me? Any help is appreciated.
Stock iron '68 4 barrel intake, gasket matched. Stock Steel intake gasket and valley pan. Ive been running various Quadrajets. The closest approximation would be a 72 800cfm unit. 73 jets 44 rods, ck 2ndary rods. My thought was that a carb issue would follow the planes of the intake and stagger the issue in the cylinders. A carb base gasket leak would do the same. The only way to get progressively leaner, front to rear - ASSUMING that is the problem - would be to have progressively greater vacuum leakage front to rear. Or maybe it has to do with flow inside the intake and heads. The heads had a valve job, were gasket matched, and the ports were cleaned up some. I cant make sense of it.
The only thing I can think of is that maybe you were running on the primaries most of the time and the rear cylinders were leaning out and running hot.
