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Mercury Outboard Ignition Parts

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Boating Know How
Ignition Parts and Systems

Ignition Parts and Systems

The ignition system is a necessity in every boat engine – it is what causes the flywheel to rotate and spark the engine into motion. Every part of an ... read more ignition system contributes to creating an electrical current, which collects in the stator, then switches to the power pack, then moves into the ignition coils. All of this collected electricity then begins to travel from the ignition coils through the spark plug wires to the spark plugs. The spark plug then gives the spark that starts the pistons and keeps them going.


  • Spark plug and wires – sparks the fuel and air mixture, igniting and starting the engine.
  • Ignition coil – changes the voltage charge into a spark voltage ranging anywhere between 30,000-50,000 volts.
  • Ignition tune-up kit – consists of hardware and components that help to maintain/repair the ignition system. Includes contact sets, condensers, etc.
  • Stator – helps to maintain the charge in a battery, and also serves as the power supply to the ignition system.
  • Distributor – an ignition component that consists of the shaft, rotor, and rotor shaft bearings.
  • Pull start rope/rewind springs – the pull rope and rewind spring does not offer as much of a role in the ignition system. It enables you to get the engine turning fast enough to be able to start once the ignitions switch is turned on. Without the rotation of the engine, the coil, fuel and ignition can't fire.
  • Trigger Assembly – this goes underneath the stator and sends electricity to the switch box and coils, which is generated by the flywheel and stator. Sends signals to timer base to ignite at the appropriate time.
  • Wiring harness – connects the entire system together with wires; it harnesses energy between the entire system.
  • Rectifier/Regulator – maintains, controls, and distributes battery voltage energy.
  • Switch boxes – the switch box obtains, stores and releases energy in an outboard ignition system by way of a capacitive discharge. That is why these types of ignition systems are considered a "CD ignition system".

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Diagnosing Your Mercury Ignition System

Diagnosing Your Mercury Ignition System

Every Mercury engine needs the occasional troubleshoot. The process may sound intimidating, but as long as you take your time and follow the guidelines set below, you should ... read more have no trouble in determining a diagnosis on your Mercury model.

There are three primary portions in every Mercury engine that requires the most maintenance and regular inspections. The three portions are with fuel, air, and spark.

Fuel System

Unless you are a technician or a boater with several years of experience, the process of inspecting and diagnosing the fuel system may seem confusing with the first try. Exercise caution here, because a problem that occurs within your fuel system may, in reality, be a problem with the ignition system. We do encourage you to consult with a technician or a local boat dealer. It would be wise to start off with a basic checkup on all fuel system parts– don't feel you have to dive right into diagnostics. Once you have observed the entire fuel system and have determined the existence of a defect in a certain system, you can either repair or replace the parts. Some of the more crucial components that require regular upkeep and repair are carburetors, fuel pumps, and fuel lines and connections. Do not jump to the conclusion that everything needs replacing; only the parts in critical disrepair should be replaced, not repaired. Some of the issues that could be contributing to faulty venting, loose connections, low supply between cylinders to the fuel pump, etc.


Checking the compression section of your engine is undoubtedly one of the most important things to check off your list. Checking the compression system is something that needs a thorough inspection. Performing a compression is recommended, but even a good compression test reading can overlook certain problems. After testing it, we do recommend that you inspect the system (as you did with your fuel system) to verify whether or not there are any defects or breaks in any of the parts. Some of the parts you should pay especially close attention to in your observations are pistons, rings, and cylinders. Check for wear and tear, as well as the status of the internal structure. Perform a leak down test to determine the status of all of these components. Before the diagnostic test, make sure that the flywheel and all other components are securely fastened down. If you receive negative results, it may indicate idleness and damage in the compression system. If the compression/air system does need repair, a standard winterization cleanup will help to repair damage and prolong the life of this section, as well as the life of the engine as a whole.

Ignition System

Some boaters are under the impression that the ignition system in an outboard marine engine is similar or identical to the layout in a standard automobile – however; this is not the case. Marine engines are unique in design and function, so be cautious when proceeding to inspect the ignition system. The status of the ignition system is especially crucial in the performance of the engine because it is all about timing and sparking the entire motor into action. Do not attempt to replace any damaged parts from the start, because ignition parts can be very expensive to replace. If the damage is mild enough, it can be repaired easily enough. However, if you are new to this, we do not recommend that you attempt this alone.

Please note, seek advice or guidance from a technician before attempting to diagnose and troubleshoot your engine.

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Power Packs and Spark Plugs

Power Packs and Spark Plugs

This article talk about troubleshooting and diagnosing your Power Packs and Spark Plugs. It covers Heat Ratings, Fouling, Overheating, Troubleshooting Ignition Modules, Basic Check-Up, and Exercising Safety. ... read more

When to Replace Spark Plug Wires

Spark plugs and spark plug wires are engine parts that should be regularly inspected or replaced. There are a few warning signs that may indicate that the components may need replacing immediately.

Heat Ratings

Some of the most important factors to keep an eye out for with heat rating complications are:
  • If the position setting for the insulator tip has fallen out of place.
  • If there is sign of inactive thermal conductivity with insulator components.
  • If the overall inner structure appears to be wearing down or is damaged.
  • If there is any defect with the insulator nose.


The fouling process, also known as carbon fouling, happens when the spark plug end doesn't react to the designated temperature (approximately 842 degrees Fahrenheit). If this happens, then the carbon deposits will not be able to burn/fall off of the insulator nose. In short, if this minimum temperature is not reached, the carbon deposits will begin to collect and clump together on the nose and clot, resulting in a misfire and more fouling or collecting. Furthermore, if the heat range is too low or cold, fouling may also occur, specifically when the engine is at low speed or is operating in cold environments.

If you see any signs of carbon fouling in your spark plugs, this could cause damage to the entire engine, and it will not function as it should. You should clean either the spark plug (if the case is mild enough) or replace it completely, then determine the cause of the fouling.


Overheating is one of the more common probabilities for the need of spark plug replacement. Here are some of the things to check if this appears to be a possibility:
  • If the heat range is too hot.
  • If the air to fuel ratio/mixture is very low.
  • If there are too many chamber deposits.
  • If there is a lack of lubrication or cooling.

If the engine exceeds approximately 1472 degrees Fahrenheit, then your engine is at a high risk of overheating. Spark plugs that are not clean or have been susceptible to fouling can easily begin the process of an overheating engine. If you begin to see signs of this, make sure you check the status of your spark plugs, among a few other standard procedures. Consult with a technician if necessary, especially if you are new to boating.

Troubleshooting Ignition Modules

To start troubleshooting, you will need a few key items to run the test, specifically a spark tester and starter fluid. If your engine even briefly stalls in response to the starter fluid, then you will want to check the fuel supply/system. Otherwise, it is likely that the spark is the center of the malfunction. Use the spark tester to verify whether or not this is the case.

Basic Check-Up

After you obtain a good idea of what may be causing your engine to malfunction, you might try briefly unplugging the main harness to rule out the possibility of a faulty harness or lanyard. After you unplug it, connect a jumper cable to the battery, which will give you a good, safe source of power to the ignition system as you go.

The next thing, stand back at a safe distance because doing all of this may trigger the engine into starting (be sure that you are far enough away from the belts and pulleys). If the engine does turn on, you can shut it off by removing the jumper cable.

Exercising Safety

We do urge caution in the act of troubleshooting your engine. Any act of recklessness or neglect can result in serious injury or even death, as well as damage to the engine. Gas fumes and exhaust are very dangerous aspects of the engine, so stay clear of that and wear protective gear. Make sure you are in an environment with sufficient ventilation. If you have never attempted this before or are new to boating, we highly recommend that you consult with an experienced boater or certified technician/mechanic.
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