Originally Posted by giantbike
One hint I can give is check if the derailer will put the chain onto the smallest cog when you loosen the cable,as doing this should eliminate the effect of the cable pulling.If it doesn't,then check if the high gear limiter screw is set right for its outer limit travel,as this could be the culprit that stop your chain from going further outward.hope this helps.
Thanks heaps for that. Well, it's not the limiting screws as it wont come back from even the biggest cog. I'll try seeing what it does without the cable, but I would have thought all cable would have friction which the spring might or might not be able to overcome?