Checking Spark

This video walks you through the process step by step, including: reading plug condition, using an ignition tester, testing plug & armature, armature replacing and setting the air gap using a feeler gauge.

Over View

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

The ignition system of all small engines give a ton of trouble after the fueling system, the ignition system is the next most likely system to fail.

Checking for spark is one of the first test we do when diagnosing engine issues and listed below are the tools that make checking spark easy. Common causes of a lack of spark include:

  • Plug dirty/wet/faulty
  • Plug gap off
  • Armature (coil) failure
  • Faulty on/off switch
  • Broken flywheel key

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 some of the following tools, parts and supplies.


Ratchet 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 lot 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. Picture links to Amazon.com


Ignition tester

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

Spark Plug gapper

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

Flywheel Puller

Now this tool is a must have if you're removing the flywheel. Why would want to remove the flywheel? Sometimes the flywheel key shears, it prevents your engine starting. The key is really cheap and it's easy to fix when you've got this tool. Picture links to Amazon.com


Shear-key

OEM Briggs & Stratton shear key, pack of 3. I don't know why they pack 3, you'll only use one. Picture links to Amazon.com

Briggs & Stratton Armature

Here's a common Briggs & Stratton Armature. It replaces old part numbers #591932, 799381 and 790817.

But don't order an armature without first checking your engine number or part number. Briggs have many different armatures that look similar, ordering by sight isn't advised.

Picture links to Amazon.com


Briggs & Stratton Plug

OEM Briggs & Stratton spark plug fits many side valve engines.

Picture links to Amazon.com


Briggs & Stratton Plug

OEM Briggs & Stratton spark plug fits many OHV engines.

Picture links to Amazon.com


Honda Armature

This armature fits the most common Honda engine family - GCV 135, 160 and 190. Your Honda engine size does matter for some other parts however. The engine size is stamped into the engine above and to the left of the oil dipstick. Picture links to Amazon.com

Honda Plug

OEM NGK spark plug fits Honda GCV 135, 160 and 190. Picture links to Amazon.com

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

DVOM

Every home needs a Dvom (Digital Volt Ohm Meter). It's used to check for continuity in lawn mower wiring, and for voltage when there's a battery fitted. But don't use this tool to check spark, that will kill it. I use mine everyday. I have the previous model to this and it's still doing its job. 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

Impact Wrench

I love DeWalt, they're make quality tools. This heavy duty but lightweight 1/2 inch impact wrench makes short work of stubborn bolts like flywheel nuts and rusty blade fasteners. Upto 700 ft lbs of torque on tap, I keep one in the trunk of our family car, makes a flat almost enjoyable. Picture links to Amazon.com

Drill/Screw Gun

I use a Dewalt screw gun (also a drill) in the workshop to speed up the process of removing engine covers, carburetor bolts, Armature bolts etc. It's a brushless motor and as tough as nails, I driven over it a few times - still works great! Batteries are interchangeable and so if you have a Dewalt product already you won't need the battery. Picture links to Amazon.com

Torque Wrench

Teng 1/2 Torque wrench, fantastic tool I use it every day and mine is still going strong. A torque wrench is advised for tightening components such as flywheel nuts and blades. The torque spec of these components is very important. Picture links to Amazon.com

If you are considering buying a torque wrench, definitely check out my review of Teng torque wrench.


Piston Stop Tool

Universal piston stop tool 10mm and 14mm, used to lock the crankshaft when removing and tightening the flywheel nut. Picture links to Amazon.com
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.