Cafeen,
I am sorry for coming across so contradictory. The thing is I have had such a great experience with this thing I hate to hear people tear it down.

Yes, before it arrived I had a new Saito 125 (still lighter than your YS buy a bunch) ready to put in there. But when you pick up a wing panel and think something must be left out you start thinking maybe the manufacturer actually knew what they were doing (imagine that!). The Saito 82 is still lighter than the YS 63 so I ended up with the battery as far forward as it will go. I think the next one will use even lighter servos in the tail, like JR 3421 in place of the 9411s.

At 730 square inches most people would try to install a larger engine, and there is plenty of room in the cowling to handle it. But power to weight ratios really come into play with light models and Fliton builds light models, lighter than just about any scratch builder I know. The Saito carries this thing around like an indoor electric. Actually I have now built and flown the Inspire Mini. Without battery the Mini weighs a fraction under 16 oz!!! And this is with a well, ugh, larger motor than recommended. It flies just like the big Inspire 60 but much lighter on the controls. The configuration is slightly different but similar.

Maybe you can borrow a smaller lighter engine and make a couple flights. In that video you see the model in knife edge literally falling out of the sky, it does that like a piece of cake, then add a tiny bit of power and the decent stops, it is much fun to fly this thing believe me. It does the same sort of thing in harrier/elevator/parachute mode as well.

So put it away for a while until you get a chance to put a lighter 4-stroke engine in there. I think you will like it and it will teach you a lot about aerobatics in short order.

Jimnie