Hi Martin,
I have a KF20+JR.
This link resumes quite well the features of this sturdy little boat: https://www.listingsport.com/sailboats/kingfisher/20
If the boat has a flat sail you should replace it with a cambered one, this will improve tremendously windward performance and performance in light winds…
Another tip is to get a two stroke outboard. When up in the well, the motor lies with the cilynder down. In a four stroke engine the oil fills the burning chamber up causing seizing!
Cheers Mauro