Was given an older trainer. Believe it was built in the late 70's. Still in great shape and hardly used. Having a problem flying inverted. Need a ton of down elevator, when inverted, to barely keep the nose up. Elevator throws are about 1.2" in each direction. Am running an OS 40 LA engine and the plane has way enough power. The wingspan is about 48 inches. Normal, level flight needs about 1/4", up trim, delection to keep the model flying upright, straight and level. The CG is balanced on the main wing spar. Would it help to bring the CG aft or is the plane so inherently stable, with its design, that inverted flight in not likely? Maybe a different elevator design? the pic is provided below. Any input will be appreciated.
Thanks.........


[8D]