Ignition Systems

All material on this website, and these sections, is ©Runner Outboards LLC and is intellectual property.  You may freely distribute this information as long as it is NOT edited, and credit is given to the author.

Disclaimer: The information provided should never replace common sense or the recommendations of the OEM.  I do not assume responsibility for the use or misuse of this information.  The information provided is based on my experience working as a full time mechanic, on hundreds of motors over time, reading a lot of manuals, education, and consulting other experienced mechanics along with a number of retired service reps I am friends with.
If I can offer any advice from experience, it would be NOT to try and fix your own motor if you don't have a good understanding of what you're doing.  You need to have the right special tools, reference materials, and most importantly, UNDERSTANDING of what is wrong and how to properly fix this issue.  Most people do more harm then good if just messing around blindly.  The reason why I can do these repairs is I've put in thousands of hours reading, fixing, and practicing.  I learn something new everyday.  I have also gone out and acquired the necessary, CORRECT tools and reference manuals to work on the motors.  These are very important to promote correct operation of the motor.  The idea is to have a reliable motor, not just one that 'kinda runs.'

Index - Click below to Jump to That Section

Internal Combustion Essentials
The Basics, What You Need To Know About Motors

Cooling System
Gearcase Components
Ignition System
Fuel System
Mechanical Components
Trailer 101

When is it Time to Change Spark Plugs?

I have to say that I hear people talk about spark plugs being the problem or solution to a wide variety of ignition problems all the time.  I'm going to have to disagree with people on this one, being a full time mechanic in the repair business.  While it is very important to have good working plugs, and even more importantly, CORRECT plugs, it is rare for spark plugs to be the sole culprit, or even the direct source of ignition problems. 

Most plugs are rated for 100's of hours of use before they just go bad.  A hundred hours on an outboard motor takes time to accumulate.  In perspective, you would need to run your motor at least 10 hours a week for 10 weeks to do this.

Spark plug heat ranges, however, are critical (to keep the motor from running too cold or overheating).  Always verify you have the right plugs for your motor.  Most OMC's from the 60's and 70's run with J4C's or J6C's.  Newer motors generally use Champion QL77JC4's or equivalents from other brands.  NGK make effective plugs.

Proper operation of your cooling system, correct oil:fuel mixture (generally 2% oil), and correct syncronization between your ignition and fuel systems all have large impacts on your plug life.  You can fry a brand new set of plugs in just 2-3 minutes if your motor is overheating due to a faulty cooling system, or if you use the wrong plugs in general.  Here are pics of worn spark plugs.  The motor ran fine, but upon normal inspection I noticed these and it was obvious that it was time for replacement.  Worn electrodes are a simple assessent 'red flag.'  They should be squared off with the tip (the hook shape).  The spark jumps this gap and then is grounded to the powerhead of the motor via the metal casting and threads.

plug1 plug2

What you CAN do, is make sure your plugs are gapped correctly.  Generally, most OMC's go for 0.30 gap.  Head on down to your local automotive store and buy a plug gapping coin (usually about $1.00).  I have run into several situations where a motor is not running right, and unless I have personally carried out repair work on the ignition and fuel systems, the first thing I check are the plugs.  If the plugs are oily, then we know the motor is running rich/blubbering (also easy to tell by just the way the motor is running).  If it run erratically, well then you may find water on the plugs, meaning you have some big problems somewhere else in the motor.  If the motor is 'missing' across low-mid throttle ranges, or even just at the top end, they may be gapped too far or improperly.

Old-time racers sometimes would gap their plugs a smaller distance if the ignition was getting weaker.  Well, this somewhat helps in a temporary situation, but it still just a band aid.  The bigger problem isn't being truly addressed.  The color of the plug tells you a lot too.  A plug that is bone dry, white, and perhaps with specks means the motor is running too hot.  This can be confirmed by using an electric laser thermometer while running too.  If the plugs are chocked with carbon (black) and caked up fuel deposits, it is running too cold and you're only on borrowed time before the plugs get fouled.  If a plug is totally soaked in fuel, then it may be dead and not firing at all, or that cylinder may not be firing off due to that side/part of the ignition sytem is dead.  Further investigation is warranted for any of these situations.

A good running motor will show a dull grey/brown chaulky appearance on the plugs.  The worn plugs pictured above shows a normal running motor, albeit the plugs needed replacement.  I pulled these plugs off of a 1993 6hp motor I had just run for the first time.  These were the original plugs as evidenced by the factory blue paint on them; so for 22 year old plugs they were still working but were overdue for renewing.  The motor ran totally fine even with these, but probably was loosing some power due to worn and overly gapped plugs, due to the wear they had on them.  It also had a newer CD style ignition, which is superior to the older magneto style.  Not to knock magnetos, as a good magneto still can create a respectable 1/2 inch bright blue spark and thousands of volts.  The electrodes should appear square, not rounded, or worn away as you can clearly see in these pictures.

If you are checking for spark, you need to crank the motor over fast enough to activate the ignition system (doing this with a long rope around the flywheel, and plugs out, usually allows for it, but if you have a big motor (80's and newer models 20hp or higher need a lot of cranking speed).  The spark should be bright blue (do it at night or in a dark area), and jump at minimum 1/4 inch for older motors, but 1/2 inch or more is desireable.

You can go out and buy new plugs, but remember the plug is the last part of the ignition system.  Almost always, the problem stems from further up your ignition system.  You might luck out and for $8, correct the issue, but don't be surprised if it's something else.  Read on below.

Weak Spark - Worn Points (Magneto Ignition)

If you have weak spark (and the only way to know this is with an air-gap tester, and a comprehensive knowledge of what your specific ignition system is supposed to be outputting), a lot of different things can contribute.  Depending on the style of ignition any number of components could be failing.  I've had situations where a pinhole in a spark plug wire caused weak ignition.  Literally, a pin hole was causing issues.  But your coils could be bad (charge or ignition coil), a weak sensor, a faulty diode in a powerpack, dirt on the flywheel magnet or rust, bad grounds, corrosion, leaking condensors, dirty/worn/bad points, the list goes on and on. 

Magneto systems are fairly simple and work on a similar principle to electric motors, however they generate their own electricity, whereas an electric motor has power introduced via an external source (i.e. battery or wall plug).  They consist of a coil, a point, and a condenser.  The coil is a metal core with many windings of copper wire.  When a magnet passes by this coiled wire it creates a magnetic field which is converted to electricity.  Points are just that - two points that transmit the power induced by the coil.  The condenser is essentially a storage vessel.  As the power is being created by the coil it holds charge, and when the point opens the power is released out through the coil and down to the spark plug, igniting the air-fuel mixture and creating combustion.  This all happens thousands of times per minute as a motor runs, and this style of ignition was used from the early 1900's and is still used even today.

When the points become dirty or worn, it interferes with the flow of electricity to where it should go and reduces the strength of the spark.  It is a relatively easy problem to remedy, but there are a lot of things necessary to restore the ignition system to a strong working condition.  Here are some examples of points that were frosted (white color), dirty (black) and broken in/somewhat worn (observe the pitting).  All three sets were salvaged after a thorough cleaning and reset.  Points have a concave/convex configuration to allow a more precise timing of spark generation.  Points that appear to have pitting or rough surface need to be replaced to allow the magneto to work properly.

fp1  fp2
p1  p2
wp1  wp2

A broken magneto cam can also be cause for erratic ignition.  After spending an afternoon double and triple checking my work, I finally noticed the culprit to this particular ignition sytem issue.  There is a cam which sits on the crank of older motors.  What this cam does is opens and closes the points at a precise moment.  Well if the cam is cracked or overly worn, this will cause everything to be wrong.  This is an usual situation, but if you've worked on enough of these you never know what you'll find next.


Weak Spark - Dead Coil

On older magnetos, dead coils are the #2 reason why spark is weak, or non-existent.  The older the coil, the likelier it is to have failed due to drying out.  They crack, and when this happens they usually short out or the internal copper windings break and the electrical field can no longe be generated.  In this picture, someone tried using a short cut of covering the coil with some sort of glue.  This is about as short-cutted as you can get, and had snowball's chance in hell of actually working.  It was picture worthy, to say the least, and I'll give the person some credit for creativity.  Albeit, completely wrong.

A cracked coil doesn't always mean it is no longer working properly.  External coils from motors circa 1974-1980 can actually be cracked and not short out, and still perform normally.  In these cases, you can take liquid tape (black neoprene dip) and seal these cracks to fix the normal insulating properties of the coil.  this is used in many cases to repair a wire than may have damage insulation to prevent arcing or leakage of current.

Here is a modern coil where the insulation had dried out and was working normally.  The motor ran as it should, and I happened to be examing something else when I noticed spark arcing through the cracks in the insulation and out the grounding strap.  Again, there was no evidence of any issues of the motor running improperly, and in fact the motor had passed all bench tests and evaluation on a test vessel.  At this point the coil should be replaced of course.
coil  coil strap

Weak Spark - Wrong Wires

One thing the manufacturer warms repair people about is identifying replacement parts of low quality substitution, or simply 'spurious' parts.  What does this mean?  It means junk parts that sort of get the job done but really aren't supposed to be used (say, automotive parts on a marine engine) or cob-job type situations.  I will say that about 50% of my time is spent fixing DIYers bad jobs, wrong jobs, or just plain stupid ideas.  As the saying goes, "Do it right, do it once." 

Here is a simple example of a bad repair job.  What makes little sense to me is that the time it would take to replace these parts with the correct ones is no different than using the wrong ones.  This motor had very low, almost no spark.  Well turns out someone decided to use automotive, fiber type spark plug wires.  I replaced these with marine copper core wires and the motor had bright blue, strong 1/2" gap spark.  Little things make a big difference and there is a reason why the manufacturer has specific parts recommended for use.  The top wire shows the copper strands.  The bottom wire shows the automotive style fiber strands.

Broken Timing Cam

Most motors have some sort of cam which regulated the amount of fuel flow based on motor RPMs.  In carburated motors, this timing is absolutely critical so that the ratio of fuel mixture stays in syncronization with ignition spark.  It is so important, that a motor can actually not run at all, or very poorly, when set wrong.  Newer CD ignitions automatically set some of this timing, and modern day motors use EFI (electronic fuel injection) coupled with sensors to adjust the fuel to spark timing for optimum performance.  Newer motors can be up to 80% more economic on fuel at idle and low RPM's than carburated motors (watch the video on the homepage I took, entertaining).

Here is a broken timing cam from a 9.5hp motor. This probably could be repaired with epoxy if you cannot find a replacement, but the curve must remain the same as original.  That divot is there, for who knows why.  These cams can become worn over long periods of time, and this is not a part you can do without in 100% good working shape. 

broken cam

Corroded Connectors

The creating of electricity in your ignition is only as good as the delivery system by which it travels.  Electricity is like water; if it travels through a pipe and the pipe is solid, the same amount you pour in one end should show up on the other end.  If there is less, you have to look for where it is leaking out. 

Older style magnetos are relatively simple; you need good grounds (which is the entire magneto plate/stator assembly) and good connections on the coil to plug wires and plug terminals to spark plugs.  These are the most common areas for reduction of spark strength due to leakage.  Old wires that are dried out and taken permenant form need to be replaced.  While the insulation may appear intact, voltage is lost as it leaches out and finds grounds upstream of the spark plug/boot.  If you crank a motor in a completely dark room, you may be able to see these spots.  Remember electricity will generally pick the shortest distance between two points to arc; this is why many buildings have lightning rods on their grounds the electricity in a more predictable path to help shield the building from damage.

Newer style CD ignitions are considered 'solid state' in that they are encapsulated to avoid exposure to moisture and elements.  Their main vulnerabilities are at the connections, as shown below.  You can see the green corrosion, and the picture on the left actually shows salt corrosion.  This happens when carelessly left exposed to weather, or in non-stop salt exposure. 

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This particular customers entire vessel had issues with electrical systems as the previous owner he bought it from did not maintain the boat.  The picture below is a real head-shaker.  Apparently the forward controls did not have a wire long enough to reach from the helm to the motor, so someone decides to splice wires onto the remote controls.  the problem is that they used quick splices to connect the wires.  This may seem to work, but is the wrong way to do things.  The splicing should have been with shrink-wrapped butt connectors and then coated with a marine based liquid rubber or silicone to minize water intrusion/corrosion.  They wrapped the wires in a zip lock back and then a 2nd layer with a grocery bag, then agian with duck tape.  This bundle was sitting in the bilge well near the fuel tank.  Lucky there weren't any explosions!
bad splice

Corrosion is limited to just connectors.  It can also interfere with grounding of coil leads.  Some coils have a strap built into them to ground to the block, others have a wire coming off which is than screwed down to the block.  Below is a coil with a corroded strap, which appears green.  Note that these should be shiny and cleanly grounded to the block, and then covered in a marine protectant substance to discourage corrosion.  It doesn't take long for things to be badly affected in a salty environment, either.


How Solenoids Work

Solenoids are basically coils of wire that when energized, create a magnetic field.  Generally there is some sort of metal plunger that is attracted toward this coil, creating some sort of connection or mechanical movement.  Older outboards have choke lever solenoids, which all they do is close the choke.  When this happens, it gives the motor a 'burp' of fuel rich air mixture to get the motor to fire off.

The newer you get, the less you see these, and the more you see electronic fuel primers.  These work on a similar principle but instead inject fuel into the manifold, cylinders, and possibly the rear of the carb throat.  This leads to faster starts on motors than the older style choke configuration.  The old chokes work just fine (and are still used to this day on many motorized devices), but generally take a couple of extra manual pulls.  I guess paying more money to only have to pull over a motor 1 time instead of 3 is what sells products.  Of course, the U.S.A. has the highest rate of obesity on the planet. 

Here are some pics of a typical starter solenoid.  Picture 1 (top left) is what you see normally, mounted on the motor, with the key switch harnass lead on the bottom right small pole, ground lead (to motor) on the bottom left small pole, then you have the battery positive (+) lead to the large right pole, and finally the positive lead to the starter motor, which is grounded to the block of the motor through it's mounting bracket (left large pole).  I opened this up because the wire windings had shorted out, and this particular solenoid was faulty. 


By removing the plastic cover, it reveals the internals.  You can see the high voltage poles on either side (left/right).  In the middle you have a large copper ring attached to a plunger.  Removing this plunger hardware, you can see ther is a sealed coil below (as evidenced by the plastic sealant).  The two small metal poles can be seen at the top of picture #2 (sorry, bad angle due to the reflection of my camera).  What happens is when you turn your key (or press a start button), these two poles send a small amount of voltage to flow through this magnet, pulling the plunger down (which is the 'click' you hear when you turn the key to the on position). 

The plunger drops, and connects the large copper disc and also the two larger polls, allowing the delivery of (in this case) 12 volts DC to a desired instrument.  Picture #3 shows what the plunger looks like.  The spring keeps the plunger from accidentally making the connection.  The solenoid allows the delivery of high voltage without having an 'in line' smaller switch.  Without this solenoid, the switch would need to be heavy duty enough to handle the draw of whatever is down line, and could easily burn out/melt. 

The lights in your household all work off of fairly standard voltages (generally 110v A/C).   What a breaker switch does (in your electric panel) is trips off if you turn too many things on in the same circuit, to prevent the draw from going so high that you potentially have things burn up/out.  Solenoids simply keep the higher draws going to where they need while allowing lesser beefy components to still be part of the chain.

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Here is a solenoid that worked intermittently, and tested out as OK, but from a practical standpoint, was not working properly.  I had a motor where I had to do a near total rehab on the ignition and on it's initial dry trial (testing the wiring), the starter would not kick over other than moving about an 1/8 of an inch.  I tested the solenoid and it checked out based on OEM procedures.  So apart comes the starter motor to check the brushes and commutator.  Back together and it worked properly.  But on putting the motor into the test tank, I had to repeatedly engage the key switch, and every 12th turn, the starter would work. 

Then it would work as normally expected, then not the right way.  I switched starters with one I knew was good, and it behaved the same way...without consistency.  So all fingers pointed to the solenoid, which I switched out, and the problem was solved.  By opening this unit up, it was obvious that at some point a previous owner had shorted out the ignition system as evidenced by the melting.  Who knows how, but likely a direct short by someone who didn't double check their work prior to making connections to the battery.  Note the pitting/melting in the low-voltage key switch, but that aside, the distortion/burns on the high-voltage circuit.  The reason why it was intermittent is because the physical connections on both circuits were hit or miss based on the physical condition on the components.

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Again, just because the books say it's OK, doesn't mean it's OK.  The best knowledge is what you pick up on the job.

Spark Arcing

Sometimes the issue with your motor running rough can be so simple, it is easy to be overlooked.  In many instances, motors have aging components.  Now, metal generally stands the test of time if maintained properly.  However, plastic, rubber, and other perishable components are another story.  In your FUEL system, you can plan on replacing all your lines/hoses on a semi regular basis (say, every few years).  On your IGNITION system, the rubber insulation in your plug wires and boots will dry out over time.  When the rubber dries out it is subject to cracking.  That insulation is like a water pipe with a crack in it - maybe it works, sometimes. 

Electricity will usually try to find it's way to the shortest path to a ground source.  In the instance of your motor, that starts at the charge coil, then down the power coil lead, then to a powerpack (CD ignition, or just the plug wire in old point/condenser magnetos), then to a coil, then to the plug leads.  A strong ignition can have the spark jumping as much as an inch or two to the block or another ground!

If the motor runs erratically, it's more than likely an ignition issue.  Sometimes running it at night, or with the lights turned off indoors, will quickly let you find a stray spark.  I had a motor that would run fine, but sporadically drop one cylinder, than it would come back, than drop off.  Turning off the light revealed the spark was arcing from the plug boot insulator to the block with no rhyme or reason.  Replacing the plug boot fixed the issue.  It was finding it's way through a tiny pin hole which under normal conditions would not be noticeable by the naked eye.  Note that once the spark arcs, it leaves a carbon footprint, which makes it easier to choose this path again.


Damaged Magneto

CD ignition magnetos are generally very durable and almost never go bad.  They are generally made up of a charge coil which generates electricity as a magnet in the flywheel passes by, and a trigger or sensor which tells the power pack/CD box when to fire off each cylinder. 

Occasionally these components fail, but that is uncommon.  What is somewhat more common is when physical damage causes them to fail.  Usually a wallowed out brass bearing ring (which sits on a boss on top of the powerhead) can allow some slop or wobble, and this causes the components to rub up against the spinning flywheel, physically damaging them.  This is normal wear and tear and the magneto plate needs to be replaced in this instance. 

An even more uncommon situation is if one of the screws holding any one of these components somehow shakes loose and starts bouncing around underneath the flywheel, basically acting like a minature wrecking ball, wiping out the whole magneto.  Below is an example of one where the customer had been using the motor, and suddenly the motor stops dead in it's tracks.  Nothing he did could get the motor up and running again.  The ignition system was dead.  Pull the flywheel, and it becomes very obvious what happened.  Replacing these components and the motor was restored back to normal operating condition.  Notice the shards of metal throughout, and clearly the coil and stator are badly damaged.

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