A big "me too!" goes out to you, as I just got mine up and running.
See photo archive, 1978 Motobecane Mobylette 50V :-)
Clean the fuel tank Clean the carb, replace the fuel line, replace the spark plug (Bosch Platinum works nicely.)
Mopedjunkyard.com has a rough exploded view of the carb that helped me get my carb back together after a few issues after cleaning it.
Try putting on the choke, and see if it helps, the choke is basically a bypass fuel jet, and I'll bet the passage from the fuel bowl float to the fuel jet is clogged.
One other thing to take into consideration is that carbugs.com lists a recall on ALL 1975-1980 Motobecane Mobylette Mopeds. I guess the brakes and lights aren't up to federal specs for their top speed (30 M.P.H or more) so some bikes may have some sort of a wedge block ring on the variable transmission to govern the bike down to about 20.