What you have is an airplane telling you it has a c/g perfect for stable flight. It's doing what it's supposed to do. The c/g is too far forward, move it back. If the c/g is set correctly, or close to the neutarl point, the nose should pitch up and stay there at flight idle and low rate elevator as the plane stalss straight ahead. The quality of the maneuver will be effected by vertical speed, forward speed, balance, power levels, and control surface deflections. No one thing makes it happen perfectly.