I broke in my first .63 with an APC 13x6 on my Ultra Stick. Worked great.

I now have this engine in my WM Zen 50. The 13x6 didn't work as well here as this plane likes speed more than thrust - I swapped it out for a 12x8 and have now settled for a 12x7.

BTW you *wil* see a difference with 20% + nitro fuel. WHen I first started running YS engines I did so with my usual 15% fuel. The engine ran OK, but was fussy to set and the power wasn't what I expected. Tried a gallon of 20% and whoa! More power, more consistent needle settings, etc. I'm now running 30% fuel - this gives a power boost over the 20% but the fuel economy takes a hit as I have to open the main needle a bit more.