The dellorto drip is caused from one of the inner passage lead plugs coming loose and it then dripping fuel into the venturi. It is hidden in behind another plug. You have to drill out the leaking plug and put in a new one. Problem is finding the correct lead plug to fit, these are not included in any rebuilt kit. I only remember reading this a very long time ago and maybe I am wrong but this is sort of what I remember, but maybe Bruce will also chime in.
Kevin