This is the distinctive shaped clip spring used to retain the throttle needle on original Amal Concentric (Series 6 and Series 9) carburettors.
As can be seen from the photo, it allows the needle to be clipped in the centre of the spring, where it then sits in a receptor in the throttle valve, where the main throttle spring (Item 0954) sits over the top of it to stop the throttle needle moving.