When you say "rolls" do you mean it turned on its axis that runs the length of the fuselage?
If that's the case, I don't know exactly how to fix it. I have a 900 series Mustang that I've been trying to trim and I think the trim tab I put on the left wing to keep it from spiraling into the ground to the left has actually put weight on that wing and increased its spiral. I added a trim tab (mostly for the weight) to the right wing as well as some down/right thrust and it's mostly corrected.
I have had questions about whether it's necessary to balance these airplanes laterally as well as from front to back. Maybe it's a balance issue?