I need to think more about that, but Im pretty sure the diaphragm "feels" it's pressure from the atmosphere not in the throat behind the air filter.The carb would feel a lower pressure and automatically lean the mixture as if it was flying at a higher altitude...
At least that's what happened. The Bing64 is a Constant Velocity carb.
The engine went to Norway to Edge Performance. Thomas showed us the filter was the culprit.