I agree with Dr1. The fuel line inside the tank should be flexible enough to move freely to all 4 back corners of the tank, but should NOTbe able to fold forward. An easy way to prevent the line folding forward, but retaining the flexiblity is to put a piece of brass tubing in the middle of the fuel line. If your fuel line is folding towards the front of the tank, fix that.

Also, just a quick clarification: a simple roll or loop does not really constitute "3D". And a plane with a proper fuel set-up will not cut out in 3D moves, much less a roll or a loop.