If it is the left nut you need to really tighten it use a rag in between the gears on the right side to be able to get a good tighten on it, or you can keep the spark plug in an tighten it so their is good resistance and the chain on the bike just make sure that the chain and gear cannot move.. If it is the right one their is a little screw that hold the flower nut in place so it does not spin out from the motor running.