Problem: 69' auto. Newly rebuilt 350 ran fine first 500 mi, then all of a sudden at start-up, it fouled the plugs.
History: 350, .030 over, 10:1 flat tops, high lift cam, 2.02/64cc heads, roller rockers, Performer RPM intake, 670cfm Street Avenger, Accel points dist., Mallory coil, Autolite #26 plugs, Holley mech fuel pump. All components brand new.
What I've checked: Firing order, dist cap, points, for vacuum leaks, valve adjustment, choke, floats, jets, power valve.
What I don't understand is I put new plugs in, stepped up the heat range, and didn't make a difference at all. I suspect fuel related but I am baffled. Suggestions?