Marcos I don't think lateral balance has anything to do with it at all. As I mentioned, it happens to ALL Funtana 90's. They can't all have heavy right wings.
Do that test I mentioned and see what you find out.
Sometimes aircraft designs end up with a peculiarity such as this, the right combination of thrust line, moments, wing area, P factor and other factors combine to form a built-in problem that cannot be overcome. In full scale aircraft and before computerized design assistance, many of our civil aircraft had peculiarities that were built in and pilots had to be aware of them.
Although a lot of fun to fly, the Funtana 90 does have it's faults.

3dbob