My mower Kohler 17.5 engine stopped working, when I tried to restart it it will crank but not start. It only backfires with multiple tries at starting. I've real up on it and think that the fly wheel key need replacing. What I don't know is how to do that. I know where to get the part... but I have no diagram of the engine, and I would need a step by step of how to remove and replace it. Any help would be great!