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Why Spark Plugs Can Make Or Break Your Bike


When thinking about your motorcycle and what are the most important components, would you say spark plugs is one of them? Most people wouldn’t…but they should. Because spark plugs can make or break your bike! Let’s take some time to see why spark plugs are so important and how to harness the power of your plugs in the real world.

What’s New in Spark Plug Technology?

Glancing at a modern spark plug, you’d barely see any differences between it and one from years past, but a closer look under the cladding reveals spark plugs have gotten a lot more efficient…and more expensive.

Standard plugs are designed for a much shorter life when installation is in cast-iron heads, and that cycle doesn’t require newer electrodes with gold, platinum or iridium because you replace them before they exceed this replacement interval.

Fast forward to today, and plugs are designed to last 100K miles and require these advancements in order to meet the newer longer-life specifications.

This expense is due to a number of advancements that spark plug manufacturers have incorporated into their products, things like:

Iridium - Iridium is the new “miracle metal” that is the main reason for the higher cost of premium spark plugs and is also in demand for usage in cell phones and sunglasses. What advantages does Iridium offer?

  • Iridium is up to six times harder than platinum, and has a much higher melting point which makes the plug last much longer.
  • Iridium allows for a much smaller surface area electrode, resulting in a more concentrated spark pulse and requires a lower voltage to reach ignition point.
  • Iridium is highly resistant to corrosion and demonstrates a lowered arc erosion specification.

These all seem like great things, and they are, but they come at a cost.

Example: A “standard” Honda XR250R spark plug cost is $2.50 and the “iridium” version costs $10.99, so that’s a huge price differential.

Expanded electrode surfaces - This is a fancy name for the new field of funky electrodes you see on plugs such as the Bosch “+4, +4 and IR Fusion” and the E3 “DiamondFire” plug types.

E3 claims the development of a diamond shaped design with a center electrode tip that exposes multiple edges to an engine's combustion space creates higher efficiency. And because electrical impulses naturally follow the path of least resistance, the E3 electrode provides a well-formed spark. When tested, this configuration resulted in a better burn of the compressed air-fuel mixture before the beginning of the exhaust cycle.

Bosch claims the Platinum+4's firing technology combines surface air gap technology, four “yttrium-enhanced” ground electrodes, and a heat-fused center electrode with the most platinum, creating “the most powerful spark you can buy.”

It makes sense that expanded electrode areas would provide additional areas to arc to, creating a more efficient ignition phase.

Capacitive element technology - This is a secondary advancement in spark plug technology and has been pioneered by vendors such as Pulstar.

This is simply a capacitor-type element that is contained in the body of the spark plug, and this element stores input ramp voltages until it reaches peak power, releasing the voltage to the electrode at point of best ignition. Pulstar claims that this technique increases peak power and current during the resistive phase of the spark, as well as increasing electrical to plasma transfer efficiency to over 50% from less than 1%.

Pulstar also has with inconel centerwire electrodes, which perform at higher levels than fine wire iridium electrodes, which also outperform conventional inconel electrodes found in conventional spark plugs.

In talking with Pulstar’s President and Founder, Louis Camilli, we asked: What factors make the Pulstar plug more (or less) attractive to motorcycle owners?

And his reply was:


“Because ignition of the fuel charge occurs more consistently at point of ignition signal, an improvement in combustion stability occurs delivering smoother operation and quicker throttle response. Acceleration through the gears is quicker as well as average torque increases.”

Capacitive plugs are at the high end of the manufacturer’s offerings today, but have shown some promising results in both standard and higher performance vehicles.

We used some of the Pulstar plugs as part of this article in our 2008 YZ125 and so far so good. We were going to take photos but the plug still looks brand new!

So if you replace your plugs often, do you need these more expensive alternatives?

We believe the answer in most cases is need…no, but do you want these attributes…yes!

Why? Because many ThumperTalk members own recreational use motorcycles that see short-duration, extreme heat/duty cycles in competition events like motocross, enduro and enthusiastic track days, and this places added stresses on the electrode and surrounding materials, breaking them down and in turn losing efficiency in the process.

Another advantage for these newer plugs is special nickel plating to avoid seizing to aluminum heads, so it can be money well spent.


How to select the right plug for your bike

Most motorcycles have a spark plug specification in their user’s manual, so why would you need to “select the right plug”?

While we agree that the factory recommendation is the best starting point for selecting spark plug type, readers are highly encouraged to learn how to “read the plug” to accurately provide the best model for their particular application.

Here is a reference guide to reading and selecting the right plug based on your usage:

  • Start with the factory-recommended plug for your bike, and install as instructed here.
  • Ensure you have the proper plug and check the spark gap to factory specification. If out of specification, re-gap it.
  • When gapping spark plugs, the most accurate way is to use a set of gapping pliers.
  • To open the gap, gently pull the ground electrode back. Do not force a feeler gauge between the electrodes and pry them apart.
  • If you want to close the gap, gently tap the spark plug on a solid surface to bend the ground electrode.
  • A little conductive anti-seize is recommended prior to installing in a cool engine.
  • Make sure the spark plug holes are free of any contamination and install with fingers first to guard against cross threading.
  • Screw in until finger tight and torque to factory spec for aluminum or cast iron heads.
  • Note: The crush ring (washer) provides a gas tight seal between the plug and cylinder head through the cold-hot-cold operation of the enginext

Reading Your Plugs

Now, after running your machine in a variety of RPM’s and load scenarios, extract the plug and compare against this chart below.

Keep in mind a light tan or gray color indicates your plug is performing correctly. Darker coloring, such can indicate a rich condition, a cold range plug or too large of a gap.

Continue to follow these instructions until you get your plug(s) to show the best coloration that you can achieve, using this chart as your basic guide (in the Green/OK sections).



Chart photo: NGK

Appears Oil Fouled – Possible Adjustments

Try hotter range plug (longer insulator)

Change fuel ratio for less oil and more fuel in mixture (2 strokes)

Inspect and test for valve seals/worn rings (4 strokes)


Appears Cold or Rich - Adjustments

Try hotter range plug (longer insulator)

Adjust fuel/air mixture (more air needed)


Appears Hot or Lean - Adjustments

Try colder range plug (shorter insulator)

Adjust fuel/air mixture (less air needed)



Maintaining your plugs is fairly simple. When attempting to manually clean the plug you must be extra careful, paying special attention not to change the preset gap. If you do clean the plug you must re-check that the gap is within specification.

There are purpose-built spark plug cleaners that operate off of compressed air with a small bag of silica that’s used as the cleaning material and we recommend these units over manually trying to clean the plug with solvents and wire brushes.

If you want to clean a spark plug, here’s how NGK recommends doing it:

  • If the firing end is wet, make sure you clean the spark plug with
    a quick drying cleaner. (Examples: contact cleaner or brake cleaner).
  • Sand blast the spark plug using low air pressure and use a dry compound.
  • Completely blow all the sand from the spark plug.
  • Using a wire brush clean the threads and re-gap.

The Bottom Line

Today’s new iridium based spark plugs can provide a hotter spark and a cleaner burn under many different load conditions, and can remain cleaner for longer durations than the conventional copper plug.

The new capacitive element plugs like the Pulstar have shown to provide additional benefits over the iridium plugs including moderate fuel savings and lowered hydrocarbon emissions.

The bottom line is for longer life, cleaner burns and less maintenance, using the newer types of spark plugs as described here are worth every penny.




User Feedback

Recommended Comments

Good article, but I have some things to add. There are reasons why manufacturers don't use E3, or Pulstar plugs as standard equipment. The performance gain (if any) doesn't justify the increased cost. Furthermore, I have witnessed cases where these novelty plugs can't even pass standard OEM durability tests. Pulstar's inconel alloy is not more durable than iridium either; no nickel blend outperforms iridium. Iridium has a much higher melting point. I could go on and on about Pulstar's claims... I have also seen a cross sectioned (lengthwise) Pulstar plug - and it looks nothing like what is on their website. Just had a chunk of rusty iron inside. I'm pretty sure these novelty plug manufacturers wouldn't be able to supply the OEMs with the quantity they need either. They just don't use them.

Multi-electrode plugs are sometimes used as standard equipment if the application has cold fouling problems. However, they are rarely used nowadays as the engine control is better.

Another thing - electricity follows the path of least resistance. The spark will only jump between the electrodes at one location at a time - NOT at multiple locations/electrodes at the same time! This is an old myth. Basic electrical theory puts this old myth to rest. I don't care what kind of cool videos they conjure up. Furthermore, plugs with massive ground electrodes (E3) can actually shroud the spark kernel from the air-fuel mixture and quench the flame - decreasing performance.

OEM's put the spark plugs that they use as standard equipment thru thousands of hours of testing. When you replace your plug, replace it with the OEM recommended plug. It will work the best. If your bike came with NGK, use NGK. Yes, you can upgrade to a NGK precious metal plug - like platinum or iriduim - and it will last longer. Also, if you use a precious metal, fine wire electrode plug, it's not that the spark itself is "hotter", it's that the spark kernel is exposed to more of the air-fuel mixture and there is less quenching effect (heat absorbed by the electrodes) during the initial flame propagation. (The temperature of a 20kV spark between the electrodes of a conventional plug or between the electrodes of a precious metal plug is basically the same. They are both 20kV after all.) The voltage required to jump the gap of a fine wire electrode plug and the possibility of misfire will also decrease. The idle stability will increase and combustion will be slightly more efficient. 

Lastly, DO NOT use anti-seize on the threads. It's too easy to over-torque the plug and damage it by stretching the metal shell. I have seen it many times. If you use a quality plug that is plated properly, it will never give you problems. I have been using NGK plugs for decades and they never seize in the threads as long as they are properly tightened and replaced according to the manufacturer's specified interval.


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Yes a very nice article but it seems to be more 4 stroke related and a bit - sorry - over enthusiastic. 

plugs haven't got always better they have gotten more precise depending the engine needs. Which means that the variations of plugs is now broder then before.

A plug provides a sparc that is all it does but to do so the plug has to fit the environment of the engine which is heat. 

Thus we categorize our plugs in heat ranges. 

Decades ago plugs that where made where not as perfect then today but thus could provide a bigger temperatur range where they worked zhus where eligible for a variety of rides or engines, but that has changed is not the case anymore.

Then was the demand of longer service intervals of the car industry which needed a longer lasting plug therefor Oridium plugs where invented that is all what they can last longer. 

Then there where special engines very sport related especially Alfa Romeo which started with special plubg providing more then one spark.


Whilst not always necessary this was also applied to some plugs, in need just for cars with racing engines using raving fuel and where driven with max speed. 


Then there are our 2 stroke dirt bikes. These engines are using oil and they have not an exact timing of the engine cycles thus there is an overlapping between filling with fresh mixture and fumes of an explosion leaving the combustion chamber. 


The two stroke is because of that and because he uses oil a pig in terms of ignition. 


Because the 2 stroke is so "dirty" compared to a 4 stroke and can not provide likewise perfect conditions as a 4 stroke can, plugs automatically fail easier and more often. 

A two stroke will not benefit of an Iridium or whatever super plug in general if he is not a special racing engine using racing fuel and so one. 

To a 2 stroke a standard copper plug is sufficient, but you have to choose the right tip set up to match to the combustion chamber, that is important. 

Then to the picture of the plug if they still look a bit to dark you can try out a hotter plug just one number higher and try out the engine behavior. If the engine seems to run smoother and is not failing also the plug lol right and there is no knocking in low rpm or under load you found your plug. 

If not you might look up older plugs that provide a bigger heat range. 


The green plug provides old plugs and has a tool to find out which of the older ones you can use. 

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