Harley-Davidson Bad Coil Symptoms


If your Harley-Davidson is not running smoothly, then it may be due to a bad ignition coil.

Harley-Davidson motorcycles have a specific engine setup consisting of a series of coils attached to the spark plugs. These coils provide the spark needed to ignite the fuel mixture for your Harley-Davidson motorcycle to start running.

Want to know more? Continue reading this post.


What is an Ignition Coil?

An ignition coil is a device that is attached to the spark plug. It provides electricity to the plugin to make contact with the fuel mixture and start your Harley-Davidson. If you’re experiencing trouble starting your motorcycle, there may be something wrong with the ignition coil. Most of the time, it’s best to check all items attached to your Harley Davidson ignition coil most of the time.

How does an Ignition Coil work?

When all of the coils are working properly, they provide a primary current for fuel combustion. These coils are connected to a battery and then generate an electric spark that ignites the fuel mixture. When these coils don’t work properly, it can lead to many different issues for your Harley-Davidson motorcycle, including no-start problems or cold engine stalling.

Types of the ignition coil

There are two main types of ignition coils that Harley-Davidson has. The first type is the original big Twin coil which was later replaced by a slimline coil. The big twin coil is not as durable and can break or crack, and it may also interfere with other electrical components. On the other hand, the slimline coils are much more durable and compact, which helps it keep the power lead separate from the electrical wire.

The second type of ignition coil is called a dual-spark plug coil. These coils were designed for use on Harley Davidson motorcycles with dual exhaust pipes or those Harley models designed for competition racing. This design adds another set of spark plugs to increase engine power.

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When should you replace an ignition coil?

If your Harley motorcycle is experiencing any of the following issues, then it may be time to check out the coils:

– Starts but shuts off immediately

– Engine cranks but won’t start or runs poorly

– Hard starting at low RPMs and idle speed problems. Check if there is anything wrong with the coils. If one or more of them looks burnt out, then it may be time for you to replace your Harley ignition coil.

How do you test an Ignition Coil?

You can easily test a Harley-Davidson motorcycle ignition coil by doing this simple test:

– Make sure that all of Harley’s electrical components are turned off.

– Remove the spark plug to see if there is any electricity coming out of it or not. If you don’t have a voltmeter, try hooking up an old Harley part with a known working coil and checking for voltage.

– If there is no electricity coming out of Harley’s spark plug, then you should check for voltage at the coil. Unplug all connectors and test each wire one by one until you find a good ground connection that has continuity with a working part on your Harley-Davidson motorcycle.

The Harley Davidson Bad Coil Symptoms

Engine Backfiring

When a motorbike engine backfires, it means that the combustion process is occurring in the exteriors of the engine’s combustion cylinders.

The engine cycle’s spark timing could be incorrect, which allows the unburnt fuel and air to go through the exhaust.

Backfire can also be heard if the engine is either excessively rich or lean.

To compare, lean means there is less fuel in the engine than air, whereas rich implies more air than fuel.

On the other hand, backfiring occurs when there is still unutilized fuel in the combustion cylinder after all of the gases have left. The unutilized fuel or black smoke passes through the combustion cylinder and into the exhaust pipe after backfiring.

Motorcycle Stalling

The back wheel does not have enough speed to match the engine’s RPM when the user releases the clutch too quickly.

As a result, the engine would come to a halt. In most circumstances, this happens as a result of a faulty or ineffective ignition coil.

The remaining coil would continue to produce weak sparks until it no longer had enough strength to spark the spark plugs.

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If you drive continuously for a long period of time, your bike engine may stop or not start again after shutting down.

Poor Fuel Efficiency

If your bike consumes more fuel than it should, there are several warning indications. Your motorbike will get less mileage if this occurs. Check the ignition coil for any faults because it might be faulty.

Bike Engine Fails to Start

When your engine does not start, it’s an indication of a dead coil. Single-coil engines are prone to this signal, and the engine may make some cranking noise but no sparks from the cylinders. This is due to a weak spark signal from the ignition coil.

Bike Engine Misfiring

The engine misfiring is an easy indication that vehicle ignition coils are failing. The engine produces a loud burr as it is started, indicating that it is coughing or sputtering.

When your bike moves at high speed, the engine will jerk and spit, producing unpleasant vibes. The engine may cease to start or idle when you reach the ‘stop sign.’ All of these indicators suggest that there’s an issue with the Harley ignition coil.

Rough Idling

If the ignition coil fails or is weak, it will cause several symptoms, including engine jerking, rough idling, and power issues. When your engine is accelerating, you may notice some lack of interest and hesitation. As a result, your bike will sound as though the power has been lost.

How Can I Fix My Harley’s Bad Coil?

If your Harley has a bad coil, then three possible solutions can be done to fix it.

– Replace the Coil: this is a simple and most common way of fixing Harley’s coils that have gone bad. You replace the coil with one that works properly, which can be purchased from any Harley dealership or online retailers such as Amazon, eBay, etc.…

– Repairing The Coil: another option for your Harley is to repair the coil on your own. This option may be more challenging since Harley’s coils are very complex and have many components.

– Replacing The Coil With A CDI Unit: this option requires you to remove all of Harley’s current electrical wiring, which can be quite difficult for beginner mechanics or Harley owners. In addition, Harley’s with a CDI unit has no current coils and instead will use one or more coil packs that are external to the motorcycle.

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How Much Does a Bad Coil Cost?

The cost of a bad coil will depend on the brand and model of your Harley-Davidson motorcycle. The average cost for most coils ranges from $50-$90, depending on where you purchase them from.

How frequently should the ignition coil be replaced?

The Harley Davidson service manual recommended that a Harley Davidson ignition coil be replaced every 15,000 miles. This is because Harley Davidson ignition coils are weak and will wear out over time.

What is the difference between a coil pack and an ignition coil?

A coil pack consists of one or more spark plug wires that contain a coil. For some Harley Davidson models, the ignition and fuel coils are contained in the same unit, known as an electronic carburetor.

What happens when the ignition turns hot?

When the ignition coil overheats, it will cause a Harley Davidson not to start. It will not work as well when it’s hot and will wear out sooner. In addition, Harley Davidson’s that have a bad ignition coil will emit some smoke and leave behind a black residue.

Can a bad ignition coil cause transmission problems?

A bad Harley Davidson coil can cause many transmission problems. The motorcycle will have difficulty shifting gears, and the engine may not run as efficiently. The vehicle’s idle may also become irregular and quick, which indicates that the vehicle needs a new Harley Davidson coil.

Where does an ignition coil get power?

An ignition coil gets its power from a Harley Davidson battery. The battery sends a current from one terminal to the other, causing an electric spark to feed through Harley Davidson’s primary winding and into the Harley Davidson secondary winding.

How bad is a cracked ignition coil pack?

A Harley Davidson’s ignition coil pack contains one or more spark plugs wires coated with a material that aids in conducting the electricity. When this material is cracked or worn, it will interfere with Harley Davidson’s ability to start the vehicle. If this Harley Davidson is started, there will be a high probability of not reaching a high speed. In addition, Harleys that have an issue with their ignition coils emit some smoke and leave behind some black residue.

If your Harley has been having issues starting after driving it for only a short distance, then you may want to check your Harley’s coil pack and replace it if necessary. Replacing Harley’s coil pack is not very complex and can be completed in about an hour.

Understand in 30 seconds [Conclusion]

When Harley Davidson owners experience problems with their motorcycle’s performance, it could be a bad coil.

Harley-Davidson coils are made up of one or more spark plug wires coated with a material that aids in conducting electricity.

When this coating is cracked or worn, the Harley Davidson will not start and may emit smoke and leave behind a residue if running for long periods.

Replacing Harley-Davidson ignition coils can range from $50-$90 depending on where you purchase them from.

It is recommended that Harleys have new coils every 15000 miles because they wear out over time as any other part does eventually.

If your Harley has been having trouble starting after driving only short distances, then check your Harley’s coil pack and replace it if necessary.

By Jacob - The Rider

Hi, my name is Jacob. I'm the founder of Backyard Rider Mag - a blog about motorcycles. I've studied engineering in college but decided to make blogging my career because it really aligned with what I wanted to do creatively - talk about bikes! I've been riding for 16 years now- everything from sportbikes to cruisers, dirtbikes or even dual sports. And after all these years on the road, there are still new bikes that excite me just as much as when I first started riding.

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