One thing to check........
Today, one of the guys that hangs around the airfield showed up today with a foamie Corsair he had just finished putting together. He asked me if I would check it over and maiden and trim it for him, so I agreed. I looked it over, and after realigning the horizontal stab, we decided to take it up.
I went out to the runway and prepared for takeoff, everything checked out ok. As I throttled up, the plane immediately nosed over on the prop. I went out and rechecked CG, it was correct. I attempted to fly again, same thing, right on it's nose immediately.
It turns out, when he assembled the plane, he put the main landing gear on backwards, so they were angled towards the rear of the plane instead of the front. I didn't catch it right away, but after turning them around, it took off and flew great.