If CG changing is not helping... its probably got excessive "decalage" or incorrect thrust line. (or both)

Its also possible you are not going back far enough with the CG... it can get so far back that it seems to be too far when you think about it from the normal CG discussions saying 25% MAC for trainers, 28% to 33% for most aerobatic types. I've just pushed the CG back to 45% on a Goldberg Tiger 60 and that seems to be the limit for that airplane.

Large stab areas tend to allow you to push the CG back further. So... keep pushing the CG back until the elevator starts to get touchy... then go forward 1/8 inch. (do this testing with low fuel in the tank... or you'll fool yourself into setting the CG too far back)