i'm not convinced .033" IFR is too large. I didn't think you could go that big on that tube, but .033" IFR with .066" IAB isn't outrageous. I think there's something else going on. I know this isn't apples to apples but this morning I took the plugs out of my '65 coronet 440 with two edelbrock AFB's. I run four .036" idle jets plus whatever the secondaries are doing and that's a lot of idle jet area. I couldn't be happier with plug burn.