I'm with banktoturn on this one. It looks like you need to put a canopy or some sort of smooth fairing over that sharp step at the front of the turtle deck. I'm sure it's messing up the airflow over the vertical fin.

I had a friend with a Kaos, similar plane. He thought it would look cool with the cockpit canopy way back towards the tail like a Geebee. It was cool, except it wouldn't knife edge. I'm betting this step on top of the fuselage would have the same effect, only worse.