Thanks to everyone who answered. The plane only has 12 degrees of elevator throw on low rates and is laterlly balanced. I had to put 8 oz. of weight on the firewall to balance on the aft end of specs or 130 mm. The battery is in the engine box and throtle servo is on the firewall so cannot move anything more forward. The plane has a saito 150 on it with a 16/8 apc prop. Not doing anything radical it will snap at 50% throttle and full up elevator on low rates from dead level flight. I have been flying 40 years and this is a first . I have had this happen many times with other planes at too much speed and to much elevator. This is my first plane of this style. I know that I am overlooking something simple. The plane cannot do even a simple square loop. Any other suggestions appreciated.