<HTML>Well, I don't about your problem specifically, but I rebuilt one of my dellortos this fall as it was always flooding so here is what I would check:
Start at the top of the fuel system and make sure the petcock is working. The screen filter around the top had corroded to almost nothing on mine and had clogged the valves. Combine this with the rust in the gas tank (since replaced!) and the petcock wouldn't shut off.
The next thing is to look at the seat of the float needle and look for grooves. Over time the needle can devlop a groove where the needle sits, and eventually it no longer seals. Also check the float itself to make sure it actually floating - try shaking it to see if its taking on fluid - you'd be surprised at how many floats get gas-logged.
This next option may or may not apply depending on how the carb is set up. On an old Lambretta Series 3 w/ an 18mm dellorto, I saw someone had cut a small drainage hole in the bottom of the air intake hose. This provided drainage for any drip-dripping gas that may end up getting through, and apparently didn't alter the performance at all.
Good luck - and I hope this helps! You might try, as a last resort, sending it out to a scooter or Italian bike shop and have them rebuild it for you. I know this isn't as much fun, but sometimes a valid option to just get back on the road!