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.


Next: What’s New in Spark Plug Technology?







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.”

Many more claims have been made about the performance aspects and potential benefits of this capacitive discharge technology and some are substantiated in at least one study that you can read here.

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.


Next: how to select the right plug for your bike



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

Next: How to read your plug



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)


Next: Spark plug maintenance







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.

Next: The Bottom-line




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.




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User Feedback

Simple physics. Gold then copper are the twobest coconductors. I will pick a copper plug everytime for a better spark. They don't last as long but the spark is hotter

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So i just bought a Ngk iridum plug for my YZ250 And this weekend will be my first time on two wheels. So.I'll be running the bike on a low RPM for while till i get the hang of things. Should i buy the regulat plug for my riding style?

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Good info!  Since I work for a major spark plug manufacturer, I thought I would add my two cents worth.  

A comment about "copper" plugs.  The reason for using copper inside the electrodes is to speed up the heat transfer from the electrodes to the shell of the plug.  Some plugs have a copper core in the center and ground electrode, or just in one or the other.  This reduces the overall temperature of the electrodes.  Simply put - using copper inside of the electrodes makes the plug more durable - less electrode erosion.  It really has nothing to do with how the electricity is conducted or the "heat" of the spark.  

The name of the game is exposure of the spark kernel to the air-fuel mixture.  Smaller electrodes (usually made of iridium or platinum) allow more of the spark kernel to contact the air-fuel around the plug.  Allowing for a bigger initial flame kernel and quicker flame propagation.  The engine runs more efficiently.  The smaller electrodes also have less of a quenching effect on the spark kernel and more spark heat energy is transferred to the air-fuel mixture.  You don't want a large, elaborate ground electrode that shrouds or quenches the spark.  A spark plug with iridium or platinum electrodes will have better ignitability and definitely last longer - especially in four stroke bikes that have less risk of oil/carbon fouling.  However, it may be easier on your wallet to use a non-precious metal (nickel) spark plug in two-stroke bikes that may foul more often. 

Also, stick to the heat ranges listed in your manual.  Heat range = the amount of heat that gets transferred from the firing end ceramic to the spark plug metal shell.  Hotter heat range = higher ceramic temperature.  A hotter heat range reduces the risk of fouling because the carbon burns off the ceramic faster.  But if you use too hot of heat range, and the ceramic gets in the 900degC range, pre-ignition can occur.  Colder heat range = lower ceramic temperature - which keeps you out of the pre-ignition range, but the plug might foul easier.  Don't risk ruining your engine by pre-ignition caused by too hot of heat range.  If your plug is fouling with the manufacturer specified spark plug, then some carb or injection tuning is needed.  Fortunately, manufacturers have tested to confirm the proper heat range for your engine, so just stick to the ones listed in your manual.     

When replacing spark plugs, never, ever, use anti-seize.  It's too easy to over-torque it.  If you buy a quality plug like NGK, then it won't corrode and seize in the threads.  Don't use anti-seize.  

One last thing, there are many gimmick plugs out there promising way more than they can deliver.  There is a big reason why most manufacturers use plugs like NGK - it's because they test the other gimmick plugs and the ignitability or durability is not as good, or even worse, they cause pre-ignition due to the poor quality of the plug.      

Can you guess which company I work for???    

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V-rider is SPOT ON in every aspect! Thank you V-rider for your contribution on this topic. 

The only input I have to share is a little more emphasis on the likely hood of fouling the fine wire electrode plugs in older mills and carbonated bikes that don't receive much TLC keeping them properly tuned.

With todays EFI, fuel mapping is so much more precise reducing the probability of fouling, increasing spark-bolt life, along with prolonged engine life between overhauls, etc.


Again, thank you V-rider.



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v-rider is dead right about copper, there is a lot of voltage but not much current involved in a spark so the electrical conductivity of materials is not as important as their heat conductivity and melting point,  copper is used to conduct heat away from tip of electrode back into body of plug and into cylinder head.   I can remember when spark plug connector caps had  a resistor in them to suppress the electrical interference created by a spark, you could also get carbon cored leads which did same job.  Iridium is so good because it resists the combustion heat and spark erosion so well (it is spark erosion moving metal from negative  to positive electrode that opens up the gap on the plug, making the spark longer and thinner (less effective and and more easily blown out) and stressing the electrical insulation in ignition coil that causes ignition coil and system failures.  I have used NGK plugs for decades and never had a problem, they are a good honest plug that does exactly as it says on the box,  no gimmicks or sales patter - and they are nickel plated which stops them seizing in alloy heads..

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On 6/8/2015 at 1:11 PM, v-rider said:


The name of the game is exposure of the spark kernel to the air-fuel mixture.  Smaller electrodes (usually made of iridium or platinum) allow more of the spark kernel to contact the air-fuel around the plug.  Allowing for a bigger initial flame kernel and quicker flame propagation.  The engine runs more efficiently.  The smaller electrodes also have less of a quenching effect on the spark kernel and more spark heat energy is transferred to the air-fuel mixture.  You don't want a large, elaborate ground electrode that shrouds or quenches the spark.  A spark plug with iridium or platinum electrodes will have better ignitability and definitely last longer - especially in four stroke bikes that have less risk of oil/carbon fouling.  However, it may be easier on your wallet to use a non-precious metal (nickel) spark plug in two-stroke bikes that may foul more often. 

Also, stick to the heat ranges listed in your manual.  

I'd say stick to the recommended plug in your manual, not just recommended heat range. Platinum & Iridium are not recommended for my bike. I did some research on this... thinking, i could leave them in longer, given they are great for car engines that require more effort to get to the plugs. I found the standard plug is advised as the better option over N or P, this makes sense given the manufacturer recommended it and installed it from new. 

If in doubt check the manual out. I've seen the NGK parts guides usually give two options of plugs, standard and Platinum or Iridium options.  It does not give the Platinum or Iridium for my 4 stroke 450...

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The "manufacturer recommended it and installed it from new" can be due to various reasons. The main one is cost. If the manufacturer can save a few cents - they will. Believe me, I see it all the time. (Especially the car makers.)

Other reasons to use a certain plug is because the manufacturer needs it to achieve a certain replacement interval (durability), meet emissions, idle stability, match the other ignition system components, etc. etc. the list goes on...

Many manufacturers prefer to use a precious metal plug (Pt, Ir) if they can make it cost effective and work with the level of ignition components they are using. If they can run a larger gap in the Pt plug, have acceptable gap growth (wear), and the ignition system has the energy to do it, they usually will. 

On the other hand, if they get the performance they need with a conventional Ni plug, then they will be happy to use it because it is cheaper. The bean counters have a lot of say...


Edited by Weston Patch
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True! But it doesn't explain why the current NGK online catalog doesn't list I or P plugs for this bike. It was a few weeks ago, that i was looking into the decision and i think the research i found... had something to do with the ignition system by memory.

Just did another online search now though the website of NGK and it only lists CR8E (This for Wr450f 2007 to current year 2017's).   Either way, whats in there now I've replaced at 1200 kms and it looked good. So i'm happy. 


Edited by surfez

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Not sure what catalog you were looking at, but if it's ngk.com, it's not our website. I looked it up on ours ( ngksparkplugs.com ), and it lists CR8EIX.

I have went Ir/Pt on all my bikes (except my old CR250). Never had a problem.

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Another comment on the plugs like Pulstar and E3. Don't waste your money. Car and powersports manufacturers do a lot of ignition system and spark plug testing. They sometimes try these sorts of plugs to see if they can live up to their claims. If these plugs are so good, why don't they eventually make it into production vehicles? Because they don't add value. They don't perform. In many cases, the durability is worse as the electrodes wear much faster. These small plug companies don't have the experience or resources to make alloys that will last. If you visit Pulstar's website, there are some links to "research" examples that are about 5 years old. 5 years and they still aren't standard equipment in any vehicle...

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