How to test and replace the ignition coil on a chainsaw

Imagine grabbing your chainsaw, ready to tame that jungle in your backyard, and it just won’t fire up. So frustrating, right? A weak or missing spark could be the sneaky culprit behind your chainsaw’s stubbornness. If you’re thinking, “Yep, been there,” then it’s probably time to give that ignition coil a look-see. Let’s walk through spotting a faulty coil, testing it, and swapping it out so you can get back to tackling those trees.

The info in this article might not match your exact chainsaw model. We do our best to provide handy advice for all sorts of DIY repairs, but different models can have their quirks. For the nitty-gritty details, it’s a good idea to check out your manufacturer’s manual or holler at us if you’ve got questions.

How the ignition coil works in a chainsaw

Your chainsaw’s ignition coil is like its heartbeat, it pumps out the high voltage needed to spark up the engine. When you pull the starter cord, the coil gets a bit of electrical energy from the flywheel’s magnet. It then amps that up, sending a powerful spark to ignite the fuel-air mix in the combustion chamber. If the ignition coil’s on the fritz, that spark doesn’t happen, and you’re left with a non-starting chainsaw or one that runs like a slug.

Signs of a faulty ignition coil

So, how can you tell if the ignition coil is giving you grief? Keep an eye out for these red flags:

• The engine won’t start or only starts when it feels like it.
• It loses power when you’re cutting through thick wood.
• It idles rough or stalls after running for a bit.
• The spark plug shows a weak spark or none at all.

These problems often point to issues in the ignition system, could be the spark plug, wiring hiccups, or a faulty ignition coil. Testing the coil will help you figure out if it needs replacing.

Safety precautions before you begin

Working on a chainsaw isn’t something to take lightly. Even when it’s off, sharp edges and moving parts can be dangerous. So, before you dive in, keep these safety tips in mind:

• If working indoors, make sure there is adequate ventilation to prevent the buildup of exhaust fumes. Carbon monoxide poisoning can be a serious risk.
• Wear insulated work gloves to protect your hands from sharp metal parts, pinching hazards and debris.
• Never attempt to service or repair while it is running or when the engine is still warm. Wait for all moving parts to come to a complete stop.
• Exercise extreme caution when working near blades, augers, or any other moving parts. Keep your hands, fingers, and clothing clear of these areas at all times.
• If the appliance has recently been used, give it plenty of time for any hot parts to cool down before working on it. 
• Empty the gas tank before beginning any work. Refill using fresh fuel. 
• Clean up oil spills right away to prevent slipping or other damage. 
• When working with wires, avoid touching any exposed wires or terminals. If you need to touch a wire, use a non-conductive tool or wear insulating gloves to prevent electrical shock.
• Take your time and don’t rush while working to prevent accidents and personal injuries.
• Work in a well-lit area so you can clearly see and access the interior parts.
• Clear your workspace of clutter and other obstacles. Keep children and pets away from the work area.
• Be gentle when handling or removing parts. Excessive force might damage the appliance or cause injury.
• Wear safety glasses when working with chemicals, dust or cleaning large debris to prevent injury. 
• When not in use, store the machine in a safe and dry location.

How to test a chainsaw ignition coil

To figure out if the ignition coil is the issue, you’ll need to check the spark and measure resistance. Using a spark tester or a multimeter can help pinpoint the problem before you replace anything. Here’s what to do:

Step 1: Locate your ignition coil

First off, remove the chainsaw’s cover or housing to access the ignition coil. This usually just means unscrewing a few bolts or screws. The ignition coil is a small, block-like piece near the flywheel. If you’re not sure where it is on your model, take a peek at the manufacturer’s manual or check out our guide on finding your appliance’s model number.

Step 2: Inspect for obvious damage

Before grabbing any tools, give the ignition coil and its wires a good look-over. Look for cracks, burns, or melted spots. Check the wire leading to the spark plug for any fraying or exposed metal. Sometimes, a damaged wire can cause the same headaches as a bad coil, so fixing or replacing those might solve your problem.

Step 3: Test spark output

A spark tester is the easiest way to see if the coil is doing its job. Attach the spark tester to the spark plug wire and ground the other end to a metal part of the engine. Then, pull the starter cord with some quick pulls. If you see a bright, consistent spark, the ignition coil is probably okay. If there’s no spark or it’s weak, it’s time to test with a multimeter.

Step 4: Measure coil resistance

Using a multimeter helps you check the coil’s resistance. This will tell you if the coil windings are broken or shorted out:

1. Set the multimeter to measure resistance (ohms).
2. Disconnect the spark plug wire from the coil.
3. Touch one probe of the multimeter to the coil’s primary terminal and the other to the ground terminal or the coil’s body.
4. Take note of the reading. Cross-check it with the ideal range specified in your manual. If it’s way off, the coil might be toasted.
5. If your coil has a secondary winding, repeat the process: one probe on the secondary terminal, the other on the coil’s body or ground terminal.

If the readings are significantly different from what’s recommended, you’ve likely found the culprit behind the spark issues. Just remember, ideal resistance values can vary by model, so double-check your chainsaw’s specifics. If you’re unsure, you can always check our repair help resources for more details.

Gather necessary tools and parts

You’ll need a few things to get started:

• A screwdriver or socket wrench to remove the chainsaw cover
• A new ignition coil that fits your chainsaw model
• A feeler gauge for setting the air gap
• A clean cloth or brush to tidy up any dirt and debris

Make sure you’ve got the right coil by double-checking your chainsaw’s model number. If you need a hand, refer to how to find your appliance’s model number. Having the correct part is crucial for a smooth replacement.

How to replace a faulty ignition coil

If it turns out your ignition coil is shot, swapping it out is the next step. Installing a new one properly will get your chainsaw purring again. Here’s how to tackle the replacement:

Step 1: Remove the old ignition coil

1. Turn off the chainsaw and disconnect the spark plug wire. Let it cool down if it’s been running.
2. Take off the top cover or housing over the engine area. Usually, it’s just a couple of screws.
3. Find the ignition coil near the flywheel. There are typically two screws holding it in place.
4. Unscrew the mounting screws with your screwdriver or wrench. Keep them safe, you’ll need them again.
5. Gently pull the coil away from the engine. Disconnect any wires connected to it. Pay attention to how it was set up, you’ll want to install the new one the same way.

Step 2: Clean and inspect the area

With the old coil out of the way, use a clean cloth or brush to tidy up the area. Get rid of any sawdust, grease, or gunk that might interfere with the new coil. Check out the flywheel and nearby parts for any serious wear or damage. A quick cleanup now can save you headaches later.

Step 3: Position the new ignition coil

1. Place the new coil where the old one was. Line up the mounting holes with the engine frame.
2. Start threading the mounting screws by hand to hold the coil loosely.
3. Don’t tighten the screws all the way just yet, you’ll need to adjust the air gap first.

Step 4: Set the air gap

The air gap is the space between the ignition coil and the flywheel magnets. Getting this right is key for proper ignition. Here’s how to set it:

1. Rotate the flywheel so its magnets are directly under the coil’s legs.
2. Slip a feeler gauge of the correct thickness between the coil and the flywheel. The thickness varies by model (usually around 0.010 to 0.014 inches).
3. With the gauge in place, tighten the mounting screws firmly but don’t go overboard.
4. Spin the flywheel by hand to make sure it’s not rubbing against the coil. Remove the feeler gauge and double-check the spacing.

Step 5: Reconnect wiring and spark plug

1. Reattach any wires or connectors to the new coil, following your chainsaw’s wiring setup. Make sure everything’s snug.
2. Plug the spark plug wire back onto the spark plug. Give it a little tug to make sure it’s secure.

Step 6: Reassemble and test

Pop the chainsaw’s cover back on, lining it up and tightening the screws. Make sure no wires are pinched under the cover. Now, it’s time to see if your hard work paid off.

1. Set the chainsaw’s switch to “on.”
2. Pull the starter cord. If it starts smoothly and runs steadily, you’ve nailed it!

Additional information

Thanks for reading! If you need replacement parts, grab your model number and head to AppliancePartsPros.com. We offer over two million parts and most orders arrive in two business days. If you need help finding the right part or placing an order, you can contact our team at 1 (877) 477-7278.

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