So, you have just installed a new coil on your lawn mower, and nothing is happening. No roaring engine, no puff of smoke, not even a spark out of the spark plug. Well, several components of the engine need to be set and connected correctly to allow your new coil to generate power to the spark plug. If just one of these isn’t right, your lawn mower will never fire up. So, let’s take a look at what these settings and connections are.
Why is There No Spark If My Ignition Coil Is Good? (The Short Explanation)
For a lawn mower coil to produce a charge, it needs to be gapped correctly to the flywheel, have a strong magnet on the flywheel, have a working ground wire, and be free of corrosion. As a result, even a minor fault with any of these things can be enough to prevent a new coil from producing a charge.
Lawn Mower Coil Good But No Spark? Check These 4 Things
As you can see, it’s not just a case of installing a new coil to get your lawn mower back up and running. There are a few other items you need to check to make sure your new coil is actually going to work. Here are four items to check if you’re having trouble with a new lawn mower coil.
Coil Air Gap
As the magnet of the flywheel passes the coil, an electron charge is generated that is sent to the spark plug. To make this process efficient, the air gap between the magnet and coil must be set to a specific distance similar to that of a spark plug gap.
In addition, the gap on either side of the coil yoke must be set to the same required distance. As a result, if the yoke distance and the overall distance are incorrect, the coil will not be able to generate the necessary electron charge.
Basically, if it’s set wrong, it will not work. So, you can test the gap using a feeler gauge. In your lawn mower service manual, you should be able to find the coil air gap distance. If you slide the feeler gauge between the coil and the flywheel magnet on your lawn mower, you should be able to measure the gap. If the gap isn’t right, then you need to make an adjustment.
Here are some examples of popular lawn mower engines and their required coil air gaps. You’ll notice how this measurement differs from mower to mower. This shows how important it is to use a feeler gauge, not a business card, as some recommend.
| Manufacturer | Model | Coil Air Gap (inch) |
|---|---|---|
| Briggs & Straton | Series 60000 | 0.006 - 0.010 |
| Kohler | Comand Pro CS4 | 0.015 - 0.023 |
| Honda | GXV160 | 0.008 - 0.016 |
| Kawasaki | FJ180V | 0.008 - 0.016 |
Flywheel Magnets
Located on the inside of the flywheel there is a magnet that passes the coil as the flywheel rotates. Now, magnets can lose their power over time, but this is minimal and not really a factor for lawn mowers. However, magnets can become loose or misplaced. So, you will need to make sure that they are still where they should be inside the flywheel.
If you take a look at your flywheel, you’ll see where the magnets are located. Usually, the magnet location is marked, or there are polished squares making it obvious. To test the magnet, hold a piece of metal, like a pair of pliers, against the flywheel and see if they are attracted. If they aren’t, then you will need to carry out a fix.
Corrosion of the Flywheel
A lot of the time, on old lawn mowers, the flywheels are made of cast iron. This means the iron is at risk of rusting and causing a weakened transfer of magnetism to the coil. The final result is a coil that appears not to be working.
If you pop off the lawn mower’s cover, you’ll be able to see the flywheel and any corrosion that may have formed. If you have a newer lawn mower, then your flywheel might be immune to rust as it is probably made of an alloy.
Coil Ground / Flywheel Ground
Have you ever wondered why the engine stops when you let go of the bail lever on the handlebar of your lawn mower? Well, this is because once you let go of the bailer lever, a ground connection is made directly between the coil and the engine/frame.
When the bail lever is pulled, the ground connection is made between the coil and the spark plug, creating a spark. So the bail lever acts as a switch to either send the charge to the spark plug or the engine/frame. This means that the coil could be constantly grounded out if there is an issue with the bailer lever ground.
So, to test the coil’s ground wire, you’ll first need to remove the ground from the coil. This is the small wire with the push-on connector. Then, disconnect the spark plug and remove it from the mower. Next, connect a spark plug tester to the lawn mower’s spark plug cable and to the engine’s metal. Now, turn over the engine and look at the light on the tester. If it lights up, then the coil ground is bad. If it doesn’t light up, then the problem is at the coil.
You need to test this way because if you leave the spark plug in and just remove the coil ground, the engine will fire up if it is a bad coil ground. But if you fire up the engine with a bad coil ground, you will not have a safe way to stop the engine.
One final check is to test the continuity of the ground wire to make sure it’s not broken. So, grab your multimeter, set it to continuity, and connect the tester cables to either end of the ground wire. You’ll have to swap out the wire if it’s not showing continuity.
How to Fix a Lawn Mower Coil with No Spark
Now that you have a new coil for your lawn mower, it’s time to get it working. So, here are the fixes to the four common reasons your coil won’t make a spark.
Gapping the Coil
To start gapping your coil, you’ll need to get a feeler gauge and find out the specific gap distance for your lawn mower engine. You’ll find this information in your lawn mower’s service manual.
To begin, line the flywheel magnets up with the coil and insert your feeler gauge. Then, use your socket wrench to loosen off the two bolts holding your coil to the engine. As soon as you loosen the bolt, the coil will pinch up to the flywheel with the force of the magnet.
Next, use your socket wrench to tighten up the two bolts. And then, finally, remove the feeler gauge and give the flywheel a spin. You need to make sure that the flywheel doesn’t come into contact with the coil.
Tools & Information Need to Gap a Coil
- Gap Distance Measurement
- Socket Wrench
- Feeler Gauge
Fix the Magnets
You’ll need to remove the flywheel to fix the magnets. So, use a socket wrench to remove the center nut from the top of the flywheel. Next, lift the flywheel off the mower’s engine. If you turn the flywheel upside down, you’ll be able to see the magnets and that they have become loose.
What you will need to do is reposition and attach the magnets securely to the engine. I have found that two-part glue is the toughest glue for the job. So, spread your glue on the contact side of the magnet and place it back onto the flywheel. I recommend letting the glue set overnight so that you’re not pulling the wheel back off again if the glue hasn’t fully dried.
Once the glue is set, replace the flywheel and re-secure the center nut. Finally, check the coil gap and put the rest of the mower back together.
Tools & Materials to Repair a Flywheel Magnet
- Socket Wrench
- Two-Part Glue
Removing the Flywheel Corrosion
If your flywheel is looking a bit rusty, then you’ll want to grab either some sandpaper or an abrasive wheel on a drill. I find that a bit of sandpaper works just as well and only takes five or so minutes.
Simply grab your sandpaper and sand the area that passes over the coil. It doesn’t need to be sanded so that it shines, but just enough to remove the bulk of the rust. That’s all there is to it.
Tools to Remove Corrosion from a Flywheel
- Sandpaper
Repairing the Coil Ground
The coil ground wire is just a short wire with a connector at each end. One end clips onto the coil, and the other end onto the bail lever mechanism. So, locate the connector on the coil and disconnect it. Then, locate the other end of the wire by tracing it back to the bail mechanism.
Once you locate it, you may find that it has a connector or maybe a ring connector. If it’s a ring connector, you’ll need to grab a screwdriver and remove the screw.
Next, grab your new wire and attach it to both the coil and the bail mechanism. Again, this is a really quick fix, but a fault with the wire can make a good coil have no spark.
Tools & Parts Required to Replace a Coil Ground Wire
- Replacement Coil Ground Wire
- Screwdriver
Leave a Reply