Gap Mower Spark Plug

This video walks you through the process of gapping your spark plug, including: reading spark plug, cleaning spark plug, gapping the plug and testing spark. 

Over View

You’ll find useful resources on this page, tips, links to tools, parts and supplies required to complete your repair.

Gapping the plug is a simple job when you know how, and it will make a huge difference to how your mower performs.

If the plug gap is too small the spark won’t be large enough to ignite the fuel mix. If the gap is too big, the spark will occur too late, if at all and puts a heavy load on the armature (coil) possible causing it to fail prematurely.

This video will have you gapping like a pro in jig time.

Before working on your mower be sure to remove the plug wire to prevent accidental starting, see “Repair Safety Video”.

Tools & Parts

To nail this procedure you may need the following tools, parts and supplies.

WD40

This is first on the list for good reason, Wd solves a ton of problems. I won't work without it, because I can't. Picture links to Amazon.com

Ratchet Tool Set

Before we can do anything, we'll need tools. I've selected this set as I own some Craftsman tools and while I have worn some out, they did do a ton of work. So I expect this set will last the occasional user quite a long time.

This set carries both metric and standard sockets and that's important, because some mowers will have both type of fastener sizes. Includes spark plug sockets. Picture links to Amazon.com

Ignition Test Tool

This tool is used to check both the spark plug and the coil for spark. Sure you can check the spark without the tool, but it's not as good, the tool is designed to stress the whole ignition system. Picture links to Amazon.com

Plug gapper tool

This tool isn't strictly necessary if you have a feeler gauge, but it's a lot easier to handle. If you haven't guessed. You use this tool to check the gap of your spark plug, simple effective tool. Picture links to Amazon.com

Wire Brush set

Steel Brass and nylon wire brush set used to clean stubborn carbon from the spark plug electrode. Brush set is good quality, various sizes will suit lots of mechanical uses, from cleaning plugs, electrical connectors, carburetor parts, cleaning rust covered fastener heads and threads. Picture links to Amazon.com

Carb Cleaner

When cleaning your carburetor you'll need this stuff. Gumming is a sticky substance that's hard to shift. The carb cleaner will remove it, however if your carb is really bad, save yourself some work, go ahead and buy a new carburetor. Picture links to Amazon.com

Feeler gauge

The ABN 26 blade feeler gauge set is marked in SAE and metric. You'll need this set to adjust valve lash and is useful when setting armature/coil air gap. You can also use it to gap spark plugs. Picture links to Amazon.com
John Cunningham
Auto Technician and Writer at | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.