Could be an air leak. However, it could be more simple. If you remove the carb from the bike, work the throttle and visual inspect the slide. Take a "sharpie" and mark the slide when it is all the way closed. Work the throttle slowly and quickly an see that the slide returns to the exact same spot every time. If it does not return to the same spot, disconnect the throttle cable and operate the slide manually. If the slide rests at the same spot everytime, its a cable issue. If it still does not return to the same spot you likely have a burr on the slide or the housing.
Since the bike is new, check with the dealer and see what they can do for you.