sparker,
You have two wires that go into the carby, one on a 45 degree angle and the other goes in the centre. On the one that goes into the centre, you push it in and then check that when you pull the throttle cable to the stop position it moves towards the other wire on the 45 degree angle.
This will short out (when they contact)the current to the spark plug causing the mower to stop. You also have an adjustment near the throttle cable housing (air filter) as well.
A more detailed information is in the manual under parts list and manuals area.