well the throttle pickup off of idle is controlled by the slide, the pilot jet and the air/fuel mixture screw so I would be looking to see if I had a partial blockage somewhere in the idle circuit or possibly an air leak somewhere.
The needle , main jet etc plays no part in throttle response off idle up to well past 1/4 throttle opening.
Try putting about 1/4 to half choke on and then blipping the throttle . If it picks up better then you have a fuel flow problem (pilot jet atomiser etc) if it is worse then you probably have an air leak problem somewhere or your pilot jet is too rich.
I'm assuming that this carb setup has worked properly previously and isn't a fresh addition ?
http://www.ducatimeccanica.com/dellorto_guide/dellorto_3_4.html