Im not sure on the overall weight of the plane. About my first 5 flights I flew the plane with a APC 16x4 and the plane flew reeeaaally slow, slower than what Im used to. So on the last flight I slapped on a 16x6 and it was night and day, and the vertical was still unlimited. But it was alot faster, not crazy fast but fast enough for me. So Im going to stick with this combo. But another thing that go me about the Saito 125, the RPM's are a lot lower than advertised. Hopefully they get better as the engine is broken in. But I like the Saito, if you really want a four stroke for the Yak but don't want to mess with a YS, go with a Saito 150, that would probably be a very nice match for your added weight, I bet you'll be pushing 10lbs once its fueled up.