I have (had, I sold it) the exact same plane in question. I used a YS140L for power running 30% nitro and a 16x12 prop. I had unlimited on that prop and more than enough power for a KE loop. I too was in the 11 lbs range. I also flew with a 17x10 with similar results, maybe a little bit better pull at lower speeds. I think the Saito 180 has comparable power to a YS140L as long as high nitro is used (~30%) and the right prop. Ditch that master airscrew prop, but don't throw it away, you can use it to stir paint. Use an APC on the plane.

I still think you are way short on rudder throw. Your 3" is only about 20 degrees throw. That might be enough to start the loop but the pull out in the last quarter of the loop might have a pucker factor of 9 with only 20 degrees of throw.