Most Engine Starting Problems can be divided into two areas: Fuel Related or Ignition Related.

• Be sure that the machine has an ample supply of fresh fuel. For 2-cycle machines that require it, mix the proper amount of 2-cycle oil into the gasoline and shake to mix completely. Never use old or leftover fuel. Store fuel in an airtight container in a cool, dry place away from sparks and flame, and keep all vents on the can closed . Bad gas is more common than you may think, especially when starting a machine for the first time in a season. Do not store gas over the winter, pour it in your car and start fresh next year! 
• If the engine is a 4-cycle, be sure the engine oil is the right type, is clean, and is at the proper level.

   

Next step is to check for spark:

• Make sure that the ignition switch is “on”, and all attachments are disengaged and that the transmission is in neutral. Most machines have safety mechanisms that will not allow them to start or even crank over (if they have electric start)if this step is not taken. Consult your owner’s manual for the starting procedure for your machine.   

• Next- check for spark by removing the spark plug and grounding the “hex” part of the spark plug to a bare metal part of the engine or buy a Spark Plug Tester (you can get these at your local parts house cheap). Remove any spilled gasoline that is nearby, then spin the engine by pulling the rope or turning the key. You should see a blue spark jump across the plug gap. If you have a good hot spark, skip to the carb section.

• If the spark is yellow and weak, or there is no spark then the first thing to do is try a new spark plug. Do not try to clean the old one.

  

  The way a Spark Plug should look

   Set the new plug gap to the proper spec (usually 0.030″) and check for spark again. If you do see a spark, install the new plug and try to start the machine. If you still have no spark next try cleaning and setting the points on older machines, or replacing the electronic ignition module on newer machines. Before replacing the old module test it by disconnecting all the  wires from the module terminal that connect to the kill switches and recheck for spark, if you see a spark a wire or switch is defective.  Also check the flywheel key. That affects the spark timing, usually the key will

  

  Worn Spark Plug

  need replacing if you strike something while mowing and the engine stops.

 Next step is to check the carb & fuel system: