Yeah, it's only supposed to fit in one way because of the groove in the throttle slide. However, I have two Motobecane's, and both of them have that groover broken off. In fact, oddly enough, I have a Moby that will only run when the slide is in backwards. Obviously that's pointing to some other gas / air issues though.
Ive also had good luck getting Moby's to run without the choke at all, so I'm guessing that his problem is the throttle. Motobecane carb is a tricky one.