Not sure exactly how much weight I need to add. I'm in the Air Force and haven't had a chance to work on it since before Thanksgiving. Plane is a Carl Goldberg Edge 540. Seems well built and very light. I put a Saito 125 up front. What I remember is that I had the C batteries as far forward (inside the plane) as I could get get them, added a regulator at the CG, extended my engine forward 3/8 inch. And still had to hang some steel blocks out of the cowl inlets. Don't know why this plane has this problem. I've reviewed the threads on the plane with no reports of the problem. I'm really puzzled.