First, I hope you're getting caps and rotors with brass contacts and not aluminum. I've burned my share of those in the past. I thought it was plug gap until you said you checked it. Is your coil supposed to have an external resistor? And if it is, is it there? They'll work for a while without it but usually burn themselves out. Just a random thought and it's probably not the answer. I guess the only question is HOW burnt are they? Obliterated or slightly less? Still sounds strange. Good luck and sorry my ramblings aren't any help...just thinking out loud (but quietly, i guess since it's only typewritten words...)
Oh yeah...you could always upgrade to D.I.S.!!!