First do what Karol said and look up the thread, there are about 60 pages to it. Second, it isn't a 90 size if it is the CG Extra, they called it a 60 size and it should have a 68 inch built up wing. I can't recall how many I have built, it is more then 6 and under 8? I haven't had mine on a scale in a while but I think it is at about 11 pounds with a YS 120 and all FGS glass parts? I could be wrong about that but when I say the CG Extra is the best of the Extras I have ever flown in any size is something I'm sure of. I have used all glow engines in them though, usually 120 four strokes either OS or YS. The best one I built used the YS 140 Sport engine. The problem you are having may be the air foil itself? It isn't the weight of the plane. They are heavy for there size but most of the weight is from the engine. In my case it is the odd ball landing gear I have on it too but it is the best flying plane I have and I'm not making any changes to it.
All answers to any questions you have should be in the thread plus photos of the plane so you can make sure it is the CG Extra you have.