Removing glue from back of fairings.

Just preparing a couple of fairings at the moment, but as they are changing colour, i want to paint the back side aswell.
Can any body tell me what to use to remove the glue? I've tried accetone and thinners so far, but with little success.
Can any body tell me what to use to remove the glue? I've tried accetone and thinners so far, but with little success.