Thanks Steve,
I more or less figured that was what I should do. I think I need to find a smaller tank that will fit in my cg range, and hopefully not change much from full through empty, or perhaps slightly nose heavy if not level, than tail heavy when empty.

I'm building a gas bird, and the easiest thing to move around for balance were my batteries. but as I am reading, I should keep my Ignition battery quite seperate from my ships battery. wich means fwd of the cg. my next solution was to play with my fuel tank location.