Outboard Ignition & Throttle Components

Boat Motor Ignition and Throttle Components Resources and Information

PartsVu is thrilled to stock a complete selection of outboard engine ignition and throttle components from some of the most trusted manufacturers in the boating industry. The ignition and throttle are crucial to any functional outboard motor. Don’t trust any off brand manufacturer when it comes to these essential engine components. Go with one of these certified marine products and keep your engine operating at peak performance for years to come. 

Looking for more marine products for your boat and outboard engine? Browse PartsVu’s products and accessories or aftermarket engine parts.

Outboard Ignition & Throttle Components FAQs

What is an ignition coil?

An ignition coil is a crucial component in an outboard engine’s ignition system. The coil takes voltage from the battery to produce enough electrical energy to create a spark in the spark plug, thereby igniting the fuel in the engine’s cylinders. The resulting motion creates propulsion needed to push the vessel through the water. 

What is a distributor cap?

Also known as an ignition cap, the distributor cap receive the ignition wires and connects them to the spark plugs. The ignition coil sends a charge through the ignition wires. This charge is transferred from metal contacts in the ignition cap to metal contacts in the spark plugs, resulting in a spark. 

Why won’t my outboard throttle up?

If your outboard motor will not throttle up, the issue may be as simple as a tangle. Debris such as fishing line, excessive seaweed, beer can rings, or nearly any other material can wrap around the propeller and its spindle. This increases the friction and causes the bog, preventing it from rotating to propel your boat through the water. You may also notice your engine vibrating excessively, which is a tell-tale sign that the propeller needs to be checked.

The fuel used for your outboard motor can be one of the primary reasons why your outboard motor is bogging down. And this is most likely caused by the ethanol content of the gas. Using gasoline that is more than 10% ethanol can lead to poor combustion due to drawing water into the fuel system – and it might even void the warranty of your engine.

Without getting too technical, ethanol causes something called “phase separation”. Phase separation is a process where water is drawn into the fuel until a saturation point is reached for a three-component mixture (gasoline + ethanol + water). This means that the ethanol and gasoline mixture will cause an uneven mixture of gasoline and ethanol in the top of your fuel tank, while the water-heavy lower portion will reduce the octane rating of the engine if this mixture reaches 

Another common reason why your engine is bogging down when you apply throttle is a clogged fuel filter. The fuel filter’s primary purpose is to strain out any debris and dirt that may reach the engine, but the fuel filter itself can become blocked if there is enough debris. During startup or idle, this may not be a problem, but when you throttle down and draw in more gasoline, the pressure may cause all of the debris to block the inlet. This, in turn, causes the fuel pump to work harder and puts strain on your motor.

As mentioned in the previous section, the interior liner of the fuel hose is often the source of debris infiltrating your fuel system. This debris bogs down outboard motors when applying throttle, causing an uneven performance. 

Over time, fuel hoses break down due:

• Heat
• UV rays from the sun
• Bad gas (high ethanol)
• Fuel left in the lines during the off-season

For most 2-stroke and 4-stroke outboard boat motors, the cooling system uses water that is circulated through the engine to regulate temperature and prevent overheating. Under normal operation, the water pump draws water into the intake grates on the lower unit, pulling water through the cavity with a rubber impeller that is keyed to the drive shaft on top of the lower unit. 

When the impeller is worn, clogged, or misshapen, the ability to cool the engine is drastically reduced. This in turn leads to the engine overheating, triggering mechanisms that prevent the engine from functioning at high temperatures. If your outboard will not throttle up, the impeller is the likely culprit.

Your outboard engine’s ignition system is responsible for igniting the gas, firing up the engine, and keeping it running. If your outboard will not throttle up or your outboard motor dies at idle frequently, chances are you may have problems with your spark plugs.

How do marine spark plugs work?

Marine spark plugs supply the spark that ignites the air-fuel mixture, creating the explosion that allows your boat’s engine to produce power. Spark plugs generate an arc of electricity across two leads which are not touching but close enough together that electricity can jump the gap between them.

How often should I change my marine spark plugs?

Boaters debate the answer to this question. Some boaters are adamant about changing their spark plugs every year or 100 hours. PartsVu recommends religiously inspecting your spark plugs annually or every 100 hours, replacing them if they are fouled or damaged, and always replacing them every 300 hours.

What should I look for when inspecting my spark plugs?

Inspecting your spark plugs relays essential information about your engine’s health and can help you address small problems before becoming big problems. Specifically, the color of the insulator firing nose tells you a great deal about your engine’s overall operating condition. Generally, a light tan or gray firing nose indicates that the spark plug is operating at optimum temperature and that the engine is in good condition. 

Suppose the insulator firing nose contains either wet or dry dark color deposits. This indicates an overly rich operating condition, that the engine is operating too cold, a possible vacuum leak, low compression, overly delayed timing, or a spark plug gap that is too large.

If the deposits are wet, this points to a failed head gasket, oil control from piston rings, or an extremely rich operating state depending on the specific liquid at the firing end.

If your engine is overheating, spark plugs may exhibit a bright white glazed or glossy insulator firing nose or include metallic speckling. This coloration can result when your engine operates at a temperature range that is too high or runs in excessively lean conditions. Additionally, improperly tightened spark plugs may contribute to spark plug overheating.

The root causes of spark plug fouling or overheating must be corrected quickly to prevent engine performance deterioration and possibly severe engine damage.

How do I change my Mercury 4-stroke outboard spark plugs?

For most applications, the spark plugs come pre-gapped, but it is advisable to re-check gap to make sure that plugs were not damaged during manufacturing or shipment.

While removing the old spark plugs, keep track of which plugs come from which cylinders.

• Note if the plug appears to be wet from water, oil, or gasoline.
•  Note if the plug exhibits evidence of heavy carbon deposits or other fowling as well as any rust – all indicative of problems.

If you were to take your engine to a dealer for your 100-hour service, they would perform a compression test by connecting a compression gauge to the individual cylinders and using the starter motor to turn over the engine. By measuring the engine’s ability to pressurize the cylinder, you can glean information about the condition of the engine internals. To perform this test at home, you will either need a remote starter button, or a friend who can turn the ignition key with the kill lanyard removed.

This cranking with the ignition disabled will also prime the fresh oil around the block, reducing friction at startup after the service. Repeat testing for all cylinders and compare results. Readings will vary from gauge to gauge, so the test is more about measuring the difference in readings with ideal results being less than 10 percent variance.

After the compression test is completed – or skipped – you can now begin installing your new spark plugs. For ease of future removal and to reduce the risk of thread damage to the cylinder head, apply a tiny amount of anti-seize compound to the threads of the plug. Use care to avoid contacting the electrode or porcelain center of the plug. Thread the plugs into the cylinder head by hand using caution not to cross thread.