I have to schedule my UFOs - otherwise nothing would ever get completed! My UFOs are created when they reach a problem point, rather than tackle the problem, it is much easier to set them aside and start a new project.
For a UFO, I will set goals of so many hours a week or target points to reach that week. To get myself past "the problem," I set a schedule and before long the project is enjoyable again. This works for me and I usually only tackle one UFO at a time. I have not had success at juggling projects as I tend to only work on the one I want to work on.
Good luck with your project.