Guys, I am trying to trim an airplane and following the NSRCA guide here : http://www.nsrca.org/TRIMA.HTM

When flying my Javelin 90, and inverted, if i bank the airplane, then the nose dips and needs a lot of down elevator to maintain a level turn. Does that mean that the CG needs to be moved back ?

Some down elevator is expected in such a scenario, right ? 

It is similar to a turn in upright flight, where you have to apply some up elevator to prevent the model from losing altitude during turns.

I am not the best person to comment on this, but if it was a "really bad CG" problem, my expectation is that you would notice it in upright flight also (and NOT just in inverted flight).

If it flies inverted with minimum down elevator in level flight, the CG is OK.

It will certainly need more down elevator while turning, as Anwar has correctly pointed out.