Troubleshooting outboard motors ignition problems

We often receive inquiries regarding the ignition problems of 2-stroke and 4-stroke outboards. Although we are always happy to try to help with the diagnosis, it can be very difficult to do so over the phone. Besides the right tools to help in the diagnosis, it is essential to understand how the ignition system of outboards 2-stroke. The following is a list of what constitutes an ignition system from start to finish.


Your boat battery is where it all starts. Outboard motors require higher cold start amplifiers than many other motors. Therefore, a dedicated marine battery with a starting capacity adapted to your outboard motor is essential. Without the correct voltage, your starter’s starter may not be able to start the steering wheel fast enough to activate your ignition system.

Key switch

To start your electric start engine, you need a key switch which opens and closes the starter relay. It also cuts the engine by short-circuiting the CDI (or electronic unit) to ground. A faulty key switch can cause all kinds of problems with your ignition system when this part is most often overlooked.

Solenoid or starter relay

The key switch sends a signal to the relay when you turn the key to start; This allows the voltage of your battery to pass through and then be amplified to the starter. If you turn your key and the starter does not start, it may be that your relay is defective.


When your starter turns, it turns your flywheel to create tension for your ignition system and the battery charging system. The magnets inside the steering wheel rotate around a stator at high speed to create alternating voltage. Broken or detached magnets on your flywheel can cause ignition problems so they are worth to be checked.


Your stator creates tension for two reasons. First, to send voltage to your CDI (also called electronic unit) to run your motor and also to send voltage to your rectifier / regulator which will charge your battery. Intermittent ignition failures or sparks can be caused by a defective stator.


The trigger is located with the stator under the flywheel. Probably the most neglected part of the ignition system, the trigger sends a signal to the CDI (electronic unit) and tells it when to release the voltage on the coil. A faulty trigger will cause no or intermittent spark and is often misdiagnosed as a defect of the CDI.

CDI (electronic unit)

Often, a faulty CDI will be responsible for an intermittent or nonexistent spark on the cylinders, you can check the CDI by having it loaned to you by a friend or a friendly professional.

Ignition Coil

When receiving the CDI voltage, the coil amplifies the voltage and transmits it to the spark plug. Defective or damaged coils will have little or no output. We see many coil failures when customers use a spark plug not suitable for the engine.

A spark plug

This is the final component of your ignition system. The spark plug receives the voltage from your ignition coil and creates a small electric spark in the combustion chamber of your engine, igniting the air / gasoline mixture in your engine and creating an explosion that turns the crankshaft and the flywheel. Spark plugs can become clogged with oil and deposition on two-stroke engines, resulting in poor spark.

Rectifier / Regulator

The regulator / rectifier converts AC voltage to DC voltage and regulates the amount of it fed into the battery. In many cases, a rectifier / regulator also sends the signal to your tachometer to indicate the engine RPM. Sometimes the first sign of a faulty rectifier / regulator occurs when your speedometer stops working, which is very common on older Evinrude / Johnson outboards.

The purpose of this article is to give you an overview of how works the majority of ignition systems on engines 2 stroke and 4 stroke. Keep these points in mind if you have an ignition problem on your engine, but remember that to properly diagnose this type of problem, a multimeter is essential for an accurate diagnosis.