I am concluding that I have the problems sorted Gizmo. I just need to run the engine in the plane again sometime tomorrow to proved that my repair of the carb mounting has in fact fixed the manifold leak. That's a good general tip and a good one to put into the inventory for future 2 stroke adventures. Not that I am planning on having too many!
Your tips have been useful, but don't seem to relate to the symptoms that I report.