This is the most logical answer. At full power, something'stwisting on the cam that's affecting timing.

 

Sounds like the roll pin that locates the advance unit and breaker cam is sheared off. There is another pin that holds things together that can be mistaken for the one that locates the unit, but it throws the timing way off.

 

Electronic ignitions are far better than points and condenser setups ... but not getting a setup that replaces the mechanical advance is a little silly. The advance mechanism is probably responsible for most of the issues I see or hear about with Ironhead ignitions.

I'd say go to a new mechanical advance unit (if replacing the electronics with one having advance built in is not an option). Sttaic time everything correctly and then hit it witl a light when cold, and again when warm to see if something is moving. If it's not moving then more than likely the lifters are too tight and a warm engine is keeping the valves open.