Also, how do you change the spark plug on a MTD lawn mower?
In respect to this, where does the spark come from on a lawn mower? Whether you start the engine with a pull rope or the turn of a key on an electric start motor, you're relying on the ignition system to produce a spark inside the combustion chamber. When you start your lawn mower or small engine, you turn the flywheel and its magnets pass the coil (or armature). This creates a spark.
Spark plugs are an essential lawn mower component that ignite the fuel-and-air mixture inside the cylinder of the mower engine. High-voltage electricity jumps the gap at the tip of every spark plug at just the right moment to trigger fuel combustion.
Ideally, most automobile spark plugs use a thread size of about 14mm thread why those of lawn mower range between 10 to 12 mm. Because of these differences in thread sizes, they just won't fit into the same hole or the unit in which the plug is to be fit in.
For most racing applications, you usually want the plug gap to be between 0.020 and 0.040 of an inch. Most engine builders seem to settle around 0.035 of an inch. Factors such as the type of ignition you run, cylinder heads, fuel and even timing can affect how much gap will work best for you.
Start the mower when it is cold, and look through the window of the tester. Observe that there is a normal spark that allows the mower to run. One of the symptoms of a bad lawn mower ignition coil appears when you are mowing the lawn and the mower gets hot and literally shuts off.