How old is the fuel and what kinda fuel was it? How about filters, basic but it hasn't been mentioned. Like Robert said it doesn't all sound like timing but would be interesting to know where you have it set and verify that you have the advance unplugged. Also verify advance is working and how much. I would also check for vacuum leaks if for no other reason to eliminate it as a factor.

Can you pedal through the dead spot and get it to open up and run like a 440 or is it pretty much flat above XXX RPM?

Careful, your character's showing!