Stock vacuum advance distributor is connected to the carb/manifold by a small rubber joint that in turn is mated to metal line that fits the distributor! If the little rubber connector is deteriorated it could allow a vaccum leak at the carb and stop the advance from working properly! the rubber connector has a 90 degree bend. When in doubt- replace it!
See 12B2095 for the straight connector, 37H4229M for pipe and VAC001 for a kit of all three. Also fits the Sprite , Mg Midget ,and Morris Minor.