First off, if it's only a carb problem, don't even THINK about junking it!
http://www.themopedjunkyard.com/gurtner.html
They have a kind of crude exploded diagram of a couple types of motobecane carbs there. Unless a motobecane's carb design is radically different from other carbs, I would say that the needle points up and goes into a little port in the body of the carburator. I'm looking at the diagram right now, and it appears to be a lot different to the carbs I'm used to seeing.
try an o ring on the plug under the jet or just make sure it's tight.