Wow

Lots of diff opinion, and I suspect lots of different levels of experience using the YS engine.

Small YS fourstrokes need to be revved. The 53 more so that the 63 but even then you should not drop below 11k.

APC 13x4 W was a good prop for me for Fun Fly, and some 3D - depending on wind conditions. If the wind is up and you are flying 3D Aero as opposed to Fun Fly you need more pitch and less of a paddle blade - move to anything betwwen 12x8 - 14x5 N for this, but keep it to narrow blades and no less that 7 pitch for 12", 5 for 13", 4 for 14".

Propellow selection is important in performance planes..... but I would steer well clear of any wood prop, and some of the makes Ive seen mentionned deserve only a stirring job for household paint !

all I can say is dont treat your 63 like a big fourstoker - sure it will be alittle noise but it needs rpm it work properly - its only a baby remember !