I pulled apart the carb on the Motobecane again today, and found that the pilot circuit was fine, but the main jet had re-clogged itself after my first cleaning. This is a pretty typical thing to have happen. I just didn't get enough of the crud out of the jet body, and the loosened crud was free to plug things up again.
Engine runs like a charm! I couldn't be more pleased. Seems to have good power, starts to really pull at about 15mph. I'm not taking it over 15 for now, as the brakes are just pathetic. Once it's warm, I can kickstart it with a single kick, on the stand.
Still need to fix the engine mounting situation. At full RPM, when the variator pulls the engine all the way back, there is a pulley that grinds on another part. Really threw some sparks. A couple other details too; brake light not working, airbox cover broken, needs a mirror and grips, etc.
Anyway, a big thanks to everyone who assisted me here. I finally got to take a ride.