We have been messing around with my son’s Coleman CT200U. Recently replaced the carb and air filter. After replacing, the engine won’t return to idle. When you let off the throttle, for some reason the top plastic part on the carb (don’t know what it is called) won’t close all the way, causing the engine to not slow down to idle. Do I need to adjust and/or lubricate something? My son rides it pretty hard and it is definitely dirty. Any advice for a novice dad would be much appreciated!