maybe the torque spring is for 50cc 2 stroke!?
though, it shouldn't be a problem to run this spring on ag50 as long as it fits on the plate and assembly is put together as it should
remove spring and try if the torque driver is moving free and is not stuck.
if original spring worked before, there is no reason why it shouldn't work now.
also, clean it thoroughly, check seals and apply high tepmerature grease