When a carburetor leaks, it is usually caused by a bad diaphragm. They get stiff and don't work. They must be very flexible. The engine is probably flooding and the fuel only comes out when you invert it. (I remember that your plane has the cylinder in the upright position.) Check all your fuel line connections but I am betting your problem is the diaphragm. I have tried and tried but never found a way to make them flexible again once they have dried out and gotten stiff. Nothing you soak them in works.

As far as the engine only going rich when you fly it, that could be caused by air pressure in flight hitting the hole in the cover over the diaphragm. The cure for that is to solder a tube into that hole, and then run a hose from there into the fuselage so it doesn't get hit with ram air from flying. If you solder a tube into that hole, make sure the side that goes towards the diaphragm is smooth so that it doesn't restrict or damage the diaphragm.

AV8TOR