I know nothing about these systems, but in reading your email I had one question come to mind.

How do you keep from going beyond the described condition (black smoke, 43 in and 54 gph)?

Sounds like a problem that would appear on NPRs Car Talk.

The manifold pressure change observation is quite intriging.

Do you suppose something with the prop govenor is contributing to your problem?

You also mentioned that you did some wing work.  Did your tank vents become obstructed in the process?

Kevin
Kevin Stallard
President
Aerial Robotics, Inc.
970.201.1804 (cell)
970.464.4855 (office)