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Pro-Users & Operators

How to Check and Service Your Spark Plug(s)

By Jim Nelson from J and J Lawn Service

The spark plug is one of the most neglected components of the engine. It's one of the easiest components to check, service and it's cost effective to replace if needed.

If this component isn't part or your scheduled maintenance, make it part of it today.

Functions of the Spark Plug

The spark plug's primary functions are to ignite the air/fuel mixture. Electrical energy is transmitted through the spark plug, jumping the gap in the plugs firing end if the voltage supplied to the plug is high enough.

This electrical spark ignites the gasoline/air mixture in the combustion chamber.

Components of the Spark Plug

When to Check your Spark Plug(s)

A lot of small engine manufacturers recommend checking them every 100 hours; check with your particular manufacturer to determine when yours should be done.

I generally check mine when doing my oil changes at 50 hours. There are no steadfast hours set for the life span of the spark plug, as many factors need to be taken into consideration.

Some of these factors include, but are not limited to:

  • operating temperatures

  • idling at low rpms

  • age / condition of the engine and its components.

Symptoms of a Bad or Faulty Spark Plug

Here are some indicators that you may have a bad or faulty spark plug.

  • Your engine idles roughly

  • Difficulty starting your engine for the first time of the day

  • Your engine misfires

  • There's a surge or hesitation in your engine

  • Increased or high fuel consumption

  • Lack of power or acceleration

How to Check and Service your Spark Plug(s)

Disconnect the battery and remove the spark plug caps from the spark plugs and remove the spark plugs.

Examine the tips of the spark plugs - when removed, this can reveal a great deal about the health and performance of the engine.

The various spark plug manufacturers have diagnostic charts you can compare your plugs to. I keep one hanging on my way in the shop.

To check and service your spark plug, follow the steps below:

  • Clean the electrodes by scraping them with a wire brush to remove any carbon deposits.

  • Inspect them for any cracked porcelain or other wear and tear.

  • Replace the spark plug with a new one if necessary.

  • Check the spark plug gap and reset if necessary.

  • Check with your engine manufacturer to determine your proper spark plug gap.

  • To change the gap, bend only the side electrode, using a spark plug tool.

  • Install and tighten the spark plug.

  • Torque the spark plug according to your engine manufacturer specifications.

  • Connect the spark plug cap and reconnect the battery.

Safety / Warning:

Stop the engine and allow it to cool down prior to servicing the spark plugs, hot components can cause severe burns.

And that's it! I hope you found this guide useful, and it helps you when it comes to inspecting and maintaining your own spark plug(s).

Jim Nelson
J and J Lawn Service
UAG Member, 2018
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