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Spark Plug

Posted by Mr Mower Parts on 7/4/2013
 Check Your Spark Plug

It's midway through the lawn cutting season, and probably time to check your spark plug on your lawnmower. It the only source of ignition on a single cylinder lawnmower engine so it's important to make sure its in proper condition.
Below is a spark plug in good shape. Slight gray color and the center electrode is still a solid shape with sharp edges (not rounded off). If your spark plug looks like this then put it back in and keep mowing.


If your plug looks like the one below where the center electrode is rounded off and wore down, then it's time to be replaced. It will make your engine run a bit hotter and be harder to start with a plug like this installed.


If you see the overhang electrode is worn back then you will get poor fuel economy and extremely rough starts. The spark has to jump a long way to get the gas vapor to fire. This is a sign you've been running on a bad spark plug for a long time.


Finally the two you don't want to ever see. If the plug is all black or all wet and oily like the ones below, then you have some other problems in the engine.The all black indicates the engine is not completely burning the fuel and may also be a sign of a leaking valve.

The oily plug means you are burning too much oil with the gas and is often caused by a cracked piston ring or something allowing too much oil into the combustion chamber. These need attention by your mechanic.


You can get your replacement spark plug here at Mr Mower Parts. Just click on the Spark Plug category in our main menu to find the right one for your lawnmower.