The 46FX uses the 40B Carb http://www.gpdealera.com/cgi-bin/wga...pgm?I=OSMG2452 and the rotor stop screw http://www.osengines.com/parts/images/25681620.jpg both determines the "track" or "path" along which the barrel rotates but can also be used to set the minimum RPM. However it is typically best left to the servo to control this point by backing off the screw to the point where the engine will cut off and then setting the endpoints of the radio system either mechanically of electronically.