A couple ways to kill the engine

With the engine running, adjust the throttle trim knob (on the radio). When it starts to idle up, loosen the idle screw on the carb about 1 to 1 1/2 turns. Now use the trim knob to adjust your idle speed. By doing this it will kill the engine when you use the reverse function. I do mine this way to kill it when bringing it in or if you need to shut it down from a distance. Or the old fashion way is to put you finger over the carb.