As others have said idle speed is the biggest culprit. What is your idle rpm? I am using more cam [ Comp 284 XE ] with a smaller engine and mine idles at 750-800 rpm. As for plugs, I use NGK BCP6ES stock # 4930 gapped at .045 with a Crane CD ignition. I did need to drill holes in the primary throttle blades in order to keep from uncovering too much of the transfer slots [ 3310 750 cfm vac sec. Holley ]. Hot spots in the combustion chamber can also cause this problem. I have Indybrock heads which of course have the same combustion chamber as your standard Eddys. I found that when I first examined them, that there were some sharp edges around the spark plug holes in the chambers. I ground them smooth along with other bits of casting flash before installing them. Timing is 18* initial, 32* total, all in by 1800 rpm on the mechanical side with 42* total including the vacuum. Hope this helps.
