Update: With a brand new 4-pin ECU, I gave the HEI a try yet again. Exact same issue. Starts and idles fantastic, rev to about 2k and it starts spluttering and backfiring severely. Radically (about 15 degrees each way) advanced and retarded timing with same results. Idle and throttle response was affected, of course but the basic issue of not being able to rev past 2k remained.
I decided to finally throw in the towel and get a pertronix conversion (version 1). If it works I will sell my HEI components at a steep discount. I'm really bummed I couldn't get it to work and completely stumped as to why.
