Unless I'm mistaken, the carb was NOT the limiting factor between the 20, 25, and 30 mph Motobecane Mobylette 50v models. The engine's porting is what determined their speed. A stock Motobecane runs a Gurtner carburetor that may need to be re-jetted depending on the porting of the engine, but not replaced if you are looking to keep things as stock as possible. Porting your engine out will be invisible to the naked eye but will allow your moped to hit the 30+ mph you are looking to get. There are some great articles on porting for Motobecane engine on the wiki pages of this website that I highly recommend if you decide to go that route. If porting your engine is beyond what you are looking to do right now, a carb upgrade may give you some extra performance however I have never heard of carbs being referred to by 'speed' the moped is capable of. I highly recommend a Dellorto 15.15 SHA carburetor. I have personally used it on several stock Motobecanes and it works much better than the Gurtner in terms of reliability and does give a little performance boost when properly jetted. This carb does require a new intake but is more or less a bolt on and go ordeal. Treats sells a package will all the parts you need and all I had to do was grind a little material off the top of the intake and everything slipped right on. Hope that helps.