And they haven't changed much since either. The new ones look like the last of the 3800s that were produced.
I got one, now I have two. An original French 3800, and the "Americanized" 4600 from 1977. They are in a class of their own. Definitely not fast or sophistcated, but truly an icon of moped development.
If you want to see more on them you can go to the Solex Owners of America Club on Yahoo. There is alot of good information there.