Troubleshooting 2 Stroke Ignition Problems

Author: Stuart Buckingham   Date Posted:30 March 2017 

The most common thing I get asked over the phone to assist with is diagnosing outboard ignition problems. Whilst I am always happy to try and help in diagnosis, it can be very hard to do so over the phone. Apart from having the right tools to assist in diagnosis, a basic understanding of how a two stroke ignition system works is fundamental. The following is a list of what makes up an ignition system from start to finish.

1. Battery

Your boat battery is where it all starts. Outboards require higher cold cranking amps than many other engines and therefore a dedicated marine battery with the correct cranking capacity for your outboard is a must. Without the correct voltage, your outboards starter motor may not be able to crank the flywheel fast enough to activate your ignition system.

2. Ignition Switch

To activate your engine and crank it over you need a switch. Every electric start outboard has an ignition switch and it will open and shut the starter solenoid. It also turns the engine off by shorting the CDI unit (power pack or switchbox) to ground. A faulty ignition switch can cause all sorts of problems with your ignition system and is more often than not overlooked.

3. Starter Solenoid

This is effectively a gate. The ignition switch sends a signal to the solenoid when you turn your key allowing it to open; this allows voltage from your battery to pass through it to the starter motor. If you're turning your key and the starter motor isn't cranking then you may have a faulty solenoid.

4. Flywheel

When your starter motor is turning over it is spinning your flywheel to create voltage for your ignition system and battery charging system. On the inside of the flywheel are magnets that spin around a stator at high speed to create AC voltage. The flywheel also spins around the trigger (or timer base) to determine your engines firing sequence or timing. Broken or loose magnets on your flywheel will cause ignition issues so they are definitely worth checking.

5. Stator

Your stator creates voltage for two reasons. To send voltage to your CDI unit (power pack or switchbox) to run your engine and to send voltage to your rectifier/regulator that will charge your battery. Engines with no spark or intermittent spark on one bank can be caused by a faulty stator.

6. Trigger

Nestled in with the stator under the flywheel is the trigger (or timer base). Probably the most overlooked part of the ignition system the trigger sends a signal to the CDI unit (power pack or switchbox) and tells it when to release voltage to the coil. A faulty trigger will result in no or intermittent spark and is often misdiagnosed as a fault with the power pack. Additionally, a faulty trigger shorting to ground will damage a power-pack so be careful if fitting a new power pack.

7. CDI Unit

Depending on your outboard brand these units will go by different names but, they will all have the same function and that is to store voltage from the stator and release it to your ignition coil when the trigger tells it to. Often a faulty CDI unit will see intermittent or no spark on cylinders and may only breakdown when your engine warms up.

8. Ignition Coil

Receiving voltage from the CDI unit the coil will amplify voltage and shoot it through to the spark plug. Faulty or damaged coils will have weak or no output. We see a lot of coil failures where customers are using a spark plug that is not recommended by the manufacturer.

9. Spark Plug

This is the last component in your ignition system. The spark plug receives voltage from your ignition coil and creates a small electrical spark within your engines combustion chamber igniting your engine's fuel and creating the explosion that drives the piston to spin the crankshaft and the flywheel where the ignition process begins over and over again. Spark plugs can foul up with oil and carbon on two stroke engines resulting in poor spark. They are by far the easiest part to check first.

10. Rectifier/Regulator

Fitting in somewhere between all this is your engines rectifier/regulator. It is always working and its job is to replace the voltage in your battery that you've lost due to engine cranking, using electric tilt and trim, running fish finders, lights or other accessories on your boat. It converts the AC voltage to DC voltage and regulates how much voltage it is putting into your battery. In a lot of cases, a rectifier/regulator also sends the signal to your RPM gauge (tacho) telling you what revs your engine is doing. Sometimes the first sign of a faulty rectifier/regulator is when your RPM gauge stops working and this is very common with older Evinrude/Johnson outboards.


There are variances here and there, but I’ve gone for the most common and basic approach on this occasion. I hope the above has given you some insight into how your outboard ignition system works. Keep these points in mind if you ever have a potential ignition problem and hopefully, it will make a diagnosis that bit easier.  But remember, in order to diagnose ignition problems properly a Digital Multimeter with a Direct Voltage Adaptor (DVA) is a must have tool for accurate diagnosis. Another very helpful piece of material is the CDI Electronics Troubleshooting Guide, click here for pages of helpful information on almost every two stroke engine.

To shop our range of ignition parts, click here.

Comments (8)

Loosing spark mariner 50hp 1995

By: on 5 August 2018
Hi outboard spares I have a problem on the top cylinder. When it runs in idle all 3 cylinders are firing, but as soon as i touch the throttle the spark on top cylinder disappers. Also a continues alarm is on I have tryed to switch the coils around, checked all wires, checked oil level sensor, boiled the temp sensor. Nothing is helping. I have tryed almost everthing i think

Outboard Spares Response
Good Day, Thanks for getting in touch. There are a few other things it could be. 1) The alarm. These engines have a small square oil module. Often when they have failed or are faulty they will send the alarm off. This could be the reason your alarm is going off, assuming it is going off almost immediately. Additionally I think the module may also limit RPM to avoid engine failure due to lack of oil, but I cannot be 100% certain. This could also explain the spark on number 1 dropping out. 2) Faulty switchbox or trigger (timer base). The other problem you may have is a faulty switchbox or trigger. If switching the coils has made no difference, then either of these 2 parts could be the culprit. You'd need to test the trigger DVA output connected and also disconnected from the switchbox. This will tell you whether the switchbox is receiving sufficient output from the trigger. I'd also be inspecting the trigger wires for any "shorts to ground". If you don't have the tools to do this then perhaps take it to a qualified Marine Technician who has the equipment to do so. Give these a try and see how you go! Cheers

1989 Mariner 90 HP 3 cylinder outboard - Top Cylin

By: on 21 July 2018
Hi, hoping you might be able to put me in the right direction. The top cylinder has spark, fuel, and compression. However it appears it is not firing. While the motor is running, if I remove the spark plug boot from cylinder 1, nothing changes. Do the same thing with cylinders 2 and 3 make a noticeable difference in the way the engine runs. The engine will stay running if only cylinder 2 or cylinder 3 has the spark plug boot on, but if only cylinder 1 is plugged in the engine dies. Not sure where to go from here. Thank you.

Outboard Spares Response
Good Day, Thanks for getting in touch. Firstly, is there an issue while the engine is running? Meaning, if you use the engine in a normal operating way does it lack power? I'm just trying to establish what lead you to trying to diagnose an ignition problem, because if the engine has fuel, spark and compression then realistically it should be running fine. If not, timing is then possibly a problem or weak spark on the top cylinder. These engines run a Coil on each cylinder . You could try swapping these around (move the top Coil to the middle and the middle Coil to the top) and see if the problem shifts to the middle cylinder. If it does shift then it's most likely a coil that is no longer performing within specification and then all you'll need to do is replace it. It's worth also checking your trigger wires going to the top coil. If you have any wires that are shorting to ground, then they'll cause a coil to play up. I hope this has been of some assistance and I apologise for the delayed response. Cheers

1989 Suzuki DT140 Outboard 2 stroke - Sputtering

By: on 19 July 2018
Motor runs fine upon starting but when giving it gas it sputters as if it is missing. Have had plug changed and carburetor checked and all seems good. The tech says it appears to be the ignition system and that this motor uses pulsars but its difficult to diagnosis. Any suggestions for how to diagnosis or repair.

Outboard Spares Response
Hmmm sounds like a curly one! I'd be getting the mechanic to check the stator output with a Direct Voltage Meter. This will allow you to see if the stator is putting out sufficient voltage. Also, a simple spark test (using a spark tester) could help in possibly identifying which cylinders are breaking down. I must admit, I'm not too familiar on Suzuki ignition systems, but it does sound like an ignition issue. If you can get your hands on a manual then that will be your best bet to resolving the problem and being able to test each component properly. Sorry I can't be of better help on this occasion.

1986 60hp mariner

By: on 15 July 2018
Hi my motor will crank over first go but if it doesn’t start first go the battery won’t crank it again , it’s a brand new battery and all the wires have been replaced if iv had it running for 10mins and turn it off same thing but if I pull start it it will start first go , iv had it in the shop about 7 times now and still same problem any advice I’d greatly appreciate

Outboard Spares Response
Hey, thanks for getting in touch. Have you had the technician strip the starter motor and check that all contacts are clean and the brushes are not worn? It's a pretty old engine and if the starter is of the same era (meaning it hasn't been replaced) then you possible have a starter motor in need of some repairs. These engines have a lot of compression and you really need a healthy starter and battery to ensure you don't have any starting woes. Let us know how you go! Cheers

2002 Mercury 90hp 2 stroke

By: on 30 June 2018
When I start the engine it runs on one cylinder but if I turn the key back about midway to off position it runs fine and I have changed ignition switch and safety switch and stator and coils any ideas

Outboard Spares Response
Good day George, sounds like a tricky one to me. It sounds like an ignition switch problem, but if you've already replaced that then it's obviously something else. I would check inside the control box and make sure nothing is loose and shorting to ground. Also, try running another engine harness (between control box and engine). Sometimes if you get moisture in the main harness it can do funny things. Otherwise, it could be your trigger (next to the stator) or your main engine loom (main loom on the engine itself). I'd be leaning towards the engine harness provided the ignition switch has been installed correctly. I hope this helps. Cheers

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