Replacement HS floats are non-adjustable: (SU Burlen)

Setting original HS float height: Only bend between the hinge pin and the float pin, a bend at the float pin may cause it to stick: (Haynes)

'StayUp' float for an HS. Image: SU Burlen

HIF: Lay a straight-edge across the middle of the body of the carb in the curve of the float. There should be a clearance of 0.5 to 1.5mm between the two at '1' below. John Twist at 2:10 here says if the weight of the float compresses the spring in the valve then the carb must be tilted so the spring is uncompressed. The WSM only says to " ... invert the carburettor so that the needle valve is held in the shut position by the weight of the float only", nothing about springs. Some valves have springs and some don't, and the effect of a compressed spring would be a lower fuel level in the float chamber:

HIF float from a carb fully reconditioned 'a couple of years' ago. Image: MGOC 'Enjoying MG' magazine and Nigel Weeks August 2016