How To Replace The Ignition Coil On A Petrol Lawnmower

How To Replace The Ignition Coil On A Petrol Lawnmower

Does your lawnmower have no spark? If so I’m going to show you how to replace the ignition coil on a petrol lawnmower. I’ve done this hundred of times over the last ten years so let me show you how. We’ll also see if it needs replacing first by doing a few simple checks.

To replace a lawnmower ignition coil, first, remove the spark plug then you will need to remove the starter recoil assembly to access the ignition coil, Spin the flywheel so the magnetic parts are away from the ignition coil then remove the screw from each side of the ignition coil. Carefully lift up the ignition coil turn it over and disconnect the kill switch wire.

Why Do You Think Your Ignition Coil Needs Replacing?

I’ve been repairing lawnmowers for profit for over ten years now and only very rarely have I had to replace an ignition coil. Usually, the reason the diagnosis of the ignition coil needing to be replaced is because the lawnmower appears to have no spark. As promised I will show you how to replace the ignition coil but first let’s eliminate a few small things that can also lead to your lawnmower having no spark.

Have You Tested For Spark?

Have you used a spark plug tester to see if you have spark? You can also set the spark plug against something metal and pull the lawnmower over to see if you have spark. If you do have spark and your lawnmower doesn’t start I can tell you with 100% certainty that the ignition coil doesn’t need replacing.

Sometimes a lawnmower can have fuel and spark and still never start as the timing is out.

usually happens when you have hit something hard with your lawnmower and sheared the flywheel key. What happens is that it moves the flywheel round slightly and although you get fuel and spark unfortunately the lawnmower won’t start as the timing is out and the spark is at the wrong time for the compression.

If you have spark and fuel on the spark plug then check the timing.

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Check The Kill Switch

Almost every lawnmower nowadays has a kill switch fitted. The ignition coil has a small wire that usually runs around the flywheel to the kill switch. If you have no spark there is a high likelihood it’s because of the kill switch.

Operate the safety lever on the handle of the lawnmower, you should see there is a metal part that moves away from the kill switch. There has to be a clear gap otherwise you won’t get a spark, it’s designed like this so when you release the safety lever the kill switch connects and stops the lawnmower engine.

Make sure everything moves correctly and is clean.

Take a look at this article for more information on kill switch problem

Swap The Ignition Coil  Wire First.

Take a look at the wire that runs around the flywheel from the kill switch to the ignition coil, is it broken anywhere? Quite often the wire gets broken if it’s not been positioned correctly.

Sometimes the recoil can push down into the wire and cause a break. If you have a spare wire try this first before purchasing a new ignition coil. You will want to keep a couple of ignition coils for spares and the connecting wires if you are going to repair lots of lawnmowers for profit over the next few years.

How To Replace The Ignition Coil On A Petrol Lawnmower

Remove the spark plug completely.

To access the ignition coil you will need to remove the pull start mechanism. Usually, this is straightforward. There will be 3 bolts to remove. 1 on the front above where the spark plug lead is, one near the back usually where the exhaust guard attaches and one more at the back near the engine oil dip stick.

Remove the oil dip stick if necessary and lift off the starter recoil.

If your lawnmower has an electric start disconnect the battery now.

You will now see the ignition coil.

Turn the flywheel so the magnetic parts are facing away from the ignition coil.

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There is usually a governor flap that attaches through the ignition coil, remove this screw and take care that the governor flap doesn’t become detached from the linkages that go to the carburettor. Remove the screw at the opposite side and carefully lift off the ignition coil and turn it over.

Pull off the wire from the underside of the ignition coil and set it aside. Next, take some photographs of the ignition coil wire so you can see exactly where it needs to go when you replace it.

Press down on the little tab on the kill switch and remove the wire.

Connect the new wire to the kill switch and put it back where the other one was. Now re-connect the wire to the new ignition coil. Take care to refit the wire in the correct position.

Note. Re-connect the wire first before attempting to re-fit and set the ignition coil.

After re-connecting the wire to the ignition coil, turn the coil back over and line up the screw holes.

Note if the coil grabs the magnets on the flywheel turn the flywheel away from the coil.

Take hold of the governor flap and place it on top of the screw hole on the ignition coil, place the screw through the governor flap and ignition coil and tighten very slightly. Take the screw at the opposite side and start to tighten slightly.

Have a good luck at the linkages on the carburettor where the governor flap connects, make sure everything moves freely and the linkages go completely through the little hole on the governor flap.

Next, take a playing card or greetings card and set it between the flywheel and the ignition coil. Turn the flywheel whilst holding the card and wait until the magnets pick up the ignition coil. You will see it jump as it tries to connect with the magnets.

  • Note. The card sets the gap between the flywheel and the ignition coil.

Tighten up both screws evenly making sure everything sits nice and even.

Turn the flywheel once more while holding the card. Remove the card when the magnets release it. This will set a nice even gap between the ignition coil and the flywheel ensuring correct spark.

Refit the recoil cover and make sure you don’t trap the new wire and refit the engine oil dipstick. Also, make sure the lead that attaches to the spark plug fits in the gap between the recoil and the engine itself.

Use the correct parts. Make sure any screws that connect the recoil cover from above are the correct length otherwise you can obstruct the governor flap.

Re-connect the battery if your lawnmower has an electric start and re-fit the spark plug.

Take a look at this video from my Youtube channel to see how it’s done.

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Check The Spark Plug Gap

It is worth taking the time to replace the spark plug at this point. I have repaired hundreds of lawnmowers in seconds by simply replacing the spark plug.

Personally, I use NGK spark plugs and have never had a problem, however, I often see new looking spark plugs that have failed. Make sure the gap is correct on the spark plug also.

Note It is possible to overtighten a spark plug to the point there is no gap. Visually inspect this and if needed set to the required specifications with a feeler gauge.

I Still Have No Spark-Help

Pull the ignition lead off the spark plug and take a look at the metal connector inside the rubber. Is it bent or squashed?

Sometimes the metal can fail as it’s only very thin and I’ve seen this a few times recently particularly on the new Briggs and Stratton engines fitted on Mc Culloch lawnmowers.

When you connect the lead to the spark plug you should feel and hear it click. If it feels slack there could be a problem.

Lastly, if you feel absolutely positive your lawnmower is getting fuel and spark and you have tried all of the above suggestions you may need to check the flywheel key on the crankshaft hasn’t sheared and thrown off the timing.

To do this you will need to remove the starter recoil, then using an impact tool remove the flywheel nut. You will need a flywheel puller to remove the flywheel and once removed you will see the flywheel key.

If there are any marks in the key whatsoever then replace it.

Even a slight mark in the key will massively affect the timing of the spark.

Lawnmower Has No Kill Switch-Help

A lot of lawnmowers, particularly Honda petrol lawnmower do not use the typical type of kill switch, they use a micro switch instead. Make absolutely sure that when you operate the safety lever you hear the microswitch click.

 If it does not click then you will not get a spark. I have picked up lots of petrol lawnmowers at auction to repair for profit where this was the only fault. I have then re-sold these lawnmowers for hundreds of pounds.

Take a look at this video to see how to replace a kill switch

Final Thoughts

It is very unlikely the ignition coil has failed on your petrol lawnmower. More often than not it is a bad connection at the kill switch or microswitch and sometimes a break in the wire.

You can check out my recommended products page to find any parts you may require here

Take a look at my article on why most petrol lawnmowers won’t  start here

Happy Mowing!


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