RE: engine rough when plane inverted
I had forgotten which engine the OS 1.55 actually was.
If the carburetor is a diaphragm-type, be sure to run a static line from the diaphragm vent port so that it opens to the atmosphere inside of the fuselage. Just the immediate pressure change that occurs around the engine when changing flying attitudes (such as upright to inverted flight) can negatively affect the fuel regulation of a diaphragm type of regulating system.
Ed Cregger