Ahhhh... good old Wikipedia. This will probably be the first result that comes up if you Google "Honda Express". Nice resource. Give you a little background into how the Express first made it onto the moped scene and why.
"The Honda motorcycle corp. of Japan released the Honda Express (NC50) to the North American market in 1977. This new bike was designed to enter the large market for mopeds that developed following the 1973 oil crisis. As such it came with a fuel efficient single cylinder two-stroke engine. It was also designed to be simple to operate, as many owners would be inexperienced with or intimidated by larger, more complex motorcycles. Honda accomplished this by using a fully automatic transmission and a small oil pump to self mix the Express's oil and fuel, thus eliminating the need for premixing."