Welcome to WF drtnsnw. I have a CX2, and they do turn one way faster than the other. Something to do with the different masses and/ or aerodynamics of the upper and lower rotors, I think. But if your's will hardly turn one way, that doesn't sound right.
I'd check for binding in one of the rotors. Also, it's a stretch, but make sure the motor connections are secure at the 3-in-1.
Stupid question, but it needs to be asked: was it like this out of the box, or were there some 'incidents' along the way? Of course there might have been some defect from the factory. Rare, but possible. If that's the case you may be best off getting it back to who you got it from with a clear description of the problem, and that it was that way WITHOUT crashing. I don't know how familiar you are with the RC hobby, but I think I've seen it's way too common for someone to wreck something and try to return it...
So where did you find a CX2 anyways? I thought they moved onto the CX3 for a few years now.