I'm pretty sure the drain screw goes on the left side of the moped, the opposite side of the choke lever. At least that's what it looks like from the manual.
Another thing, is it even possible to fit another bigger carb in there?
I have a 70 cc kit on mine and I've been thinking about getting a Delorto. But I figured that I would have to pound out the plate that the carb scrunches up against, leaving the part that is facing the wheel. You know, for more room.