Graham, People need to learn jetting somewhere. "let them figure it out" and watch people hate tuning mopeds. Tech them to jet and everyone gets 50mph and 50mph.
Elliot: Because the carb matches the size of your intake, doesn't mean it's necessarily the right size for your setup. A smooth transition from the carb to the reed is important. As little volume as you can have between the reed and the carb is an advantage. Air weighs something, and the more mass you have, the longer it takes for the air to catch up to the engines demands.
A small carb has better sensitivity. It depends wildly on how much vacuum you see. I wonder if anyone has hooked up a vacuum gauge to their moped. I may have to add a vacuum port to my Peugeot to satisfy my curiosity.
I gotta agree, not enough people realize that the pilot circuit affects all fueling ranges ;-) As for a "number slinging theroy monger who doesn't have a fast bike"... I started on a 110mph GS550, which evolved into a 130mph GS550.
If you want to talk 2 strokes, I went from a DT175, to a YZ and RM 250. The RM had no powervalve, and a DG high end pipe. That was... breathtaking. I've played with fast stuff......... I just don't have a fast moped... yet. I will.
That's waiting for me to find my files or dremmel so I can relieve my case to match the ports on my new cylinder. I know my power goals, and I have no doubt I can match them.
I wonder if anyone has considered a powervalve on a 'ped? One the one and two speed bikes, that would be a wild advantage.
Elliot: Carbs respond air flow. Not rpm. But yes, I think people around here don't put nearly enough emphasis on finding and adjusting their needles properly. If they did.. we'd hear more about tuning them. :-) If you check out dirtbike sites, you'll find that almost half the tuning is done with pilot jets and needles.