To tune A four stroke or A two stroke is the same thing, the YS only has the one extra screw and if you keep your hands off of it then there is no problem, it just regulates how much pressure is being pumped. There are the valves you need to adjust every year or two, well, not adjust but check once in A while. I'm A YS person, own OS and Saito, wouldn't be caught dead buying A Magnum.
Pick and buy the plane before you even think about the engine!! Go over to the glow engine forum and read what is going on with the engines you are thinking about. It's always nice to see what is going on from the people that are really using these engines. With all your trouble with the .55 you may want to go with something being used at your home field so you can learn how to keep the engine running buy A real person.
Good luck!!