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which ones last the longest? which ones make the best spark? which ones do you use and why? and why change them out every 10,000 miles or so when there are some that last 100,000 miles?
I use to spend the money for “splitfire” plugs long ago before I found out their “advantage” wears off too quickly. I’ve stuck with platinum plugs since then, but Amercian has me considering the new iridium plugs. I’ve heard those are what are being used that give 100k miles before time up.
Maybe we should get Bill (American) here to comment. He seems pretty up on those.
 

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bonus question: is it better to gap a spark plug towards the higher end of the recommended range or lower end?
As a rule, a properly gapped spark plug will burn hot without being too wide at high rpm to cause a misfire. Ironically, the manufacturer's recommended spark plug gap is not optimal! The recommended spark plug gap is designed to be adequate for cold starting and smooth driving on a vehicle that is in need of an engine tune up. If you drive your bike normally and tune the engine regularly, you can increase the spark plug gap by about 0.010" for better performance and better fuel economy. However, if you drive at full throttle most of the time, you should reduce the gap by about 0.010" for better performance. The spark plug itself, and the residue that forms on it, would indicate whether the gap is too big or too small. A light brownish discoloration of the tip of to porcelain insulator indicates the proper operation of the spark plugs with the gap being ideal or close to ideal for the most recent engine speeds. That being said, to check the spark plug gap at high engine speeds, you'd need to run at full throttle and immediately turn the ignition off without allowing the engine to idle. But ultimately, you'd need to run your car on a dynamometer to find the best spark plug gap, and the right ignition timing for your engine
 

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Iridium will last longer. I run standard copper and change once a year. Standard plug are cost effective even changing them more often and by changing them yearly it gives me a chance to check them for any issues such as Carb and timing. With our bikes the ignition is strong but not high performance so running recommended gap is best for driveabilty. Smaller gap is for blown or turbo applications as the added air will actually blow the spark out before combustion. Larger gap gives a better chance for ignition but can cause wear on coils as it takes more energy to make spark. On my normal asperated race motors in the past with high performance ignition a wider gap made more horsepower. Here's a guide to read plugs:

 

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Plugs are cheap. If I'm pulling them out I'll replace. Even if you put iridium plugs in at $10 bucks each that's only $20 for most of the bikes we ride here. Or $3 each for copper. Bonus is gas mileage and performance goes up with new plugs.
 

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I use the NGK Iridium plugs, and change every 3 or so years and 20K miles. Like Les said, they're cheap so I just replace, too.
 

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Spark Plugs can be a a very misunderstood item, as has been mentioned in posts above the larger the gap the more the coil has to work.

For an every day street engine with no performance mods gapping at the lower end of the spec is better because as the electrode tip wears and starts to round off the spark does not have to jump as far as it does if the gap is set at high end of the spec. This is likely not really noticeable to the driver of the car as the plug wears but as it was stated above the ignition will notice it as they can end up having to work up to 40% harder to produce the spark.

Iridium spark plug use a copper core with the tip being iridium which is a very hard metal unlike copper. Platinum is harder than copper as well and if you really want the very best longest lasting spark plug you want the Iridium plugs with the platinum buttons, those plugs are pretty much what your oems are using to get the 100,000 mile to 120,000 mile plug change intervals.

But to help you out they don't make the iridium/platinum button plugs for our motorcycles. I have searched and NGK's own cross reference does not show any.

Look at the plug chart above, what we are combating the most because we all have engines in good health is the rounding of the electrode, look at the bottom plug on the left side in that chart above, it is those rounded edges that make the coil work harder, up to 40% harder, to fire the spark plug.

An iridium spark plug because of how hard iridium is and the iridium tip is so much smaller does not wear and round off like a standard copper core plug does so over the life of the plug an iridium plug is easier on the ignition coil by not stressing it because the iridium tip does not wear out like the copper tip does.

To answer the OP question the best plug for our motorcycles is an iridium plug as it will last the longest, estimates of how long from NGK say up to two times longer than a standard plug, now that is in an automotive engine so take that into account.

If you have spark plugs that are hard to reach then an iridium plug is for you. I am not sure why Yamaha has such a low mileage for spark plug changes on the V-Twin engines in the Venture/Eluder but I am fixing to come upon the 8,000 mark where Yamaha says the plugs need to be changed.

Here is photo of an iridium spark plug new out of the box, this is what is going into my Venture.
 

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https://cartreatments.com/copper-vs-iridium-vs-platinum-vs-double-platinum-spark-plugs/

You might think that all spark plugs are the same. After all, the general purpose of a spark plug is to generate an electric current for igniting the compressed air and fuel in the combustion chamber. However, there are some differences when it comes to spark plugs. Certain ones are more efficient and perform better than others. It all depends on what type of spark plugs your vehicle’s manufacturer recommends.

All spark plugs have a central electrode and a side electrode. These electrodes were traditionally made of copper but now they are being manufactured from materials like iridium and platinum. Also, the center electrodes are being made much smaller than they used to be. This means that less voltage will be required to generate the electric current for the combustion chamber.

Overall, you will find the four main types of spark plugs are copper spark plugs, iridium spark plugs, platinum spark plugs, and double platinum spark plugs. Some have better uses than others, depending on the vehicle that you’re driving. Below you will find more details on these spark plugs and what they are good for.

Copper Spark Plugs

This spark plug is mostly made from solid copper. Its central electrode is made from nickel alloy and it has the largest diameter of all the other spark plugs. This means it’ll need more voltage to generate an electric current. Nickel alloy is a material that is soft and not very durable. This means it won’t last long. It is best to use copper spark plugs in older vehicles which didn’t have high electrical needs.

Pros – Better for older vehicles built before 1980.
Cons – They don’t last as long; Requires more voltage.

Iridium Spark Plugs

Iridium spark plugs will last the longest. Iridium is a metal that is harder and more durable than platinum. Although you will have to pay more money for iridium spark plugs, you will get what you pay for. These spark plugs have a small center electrode which means they use less voltage to generate the electric current. That is why many car manufacturers are starting to recommend iridium spark plugs for their vehicles. If you already have these spark plugs installed and you need new ones, do not downgrade to platinum or copper because they will diminish the performance of your vehicle.

Pros – Harder than platinum; Lasts the Longest; Uses Less Voltage
Cons – Expensive

Platinum Spark Plugs

A platinum spark plug is similar to a copper spark plug, except that its center electrode has a platinum disc which is welded to its tip area. The copper spark plug only has nickel alloy material in this area. As a result, the platinum spark plug is more durable and can last as many as 100,000 miles. These plugs also generate more heat, which means that debris buildup will be reduced. If you have a new car with an electronic distributor ignition system, platinum spark plugs are recommended.

Pros – Lasts longer than copper; Reduces debris buildup
Cons – Not the strongest spark plug on the market

Double Platinum Spark Plugs

If your distributor ignition system is a waste spark system, then double platinum spark plugs are recommended. This system causes the spark plugs to fire twice, once in the compression stroke’s cylinder and the other in the exhaust stroke’s cylinder. The spark for the latter gets wasted because there is no ignition there. The benefit of the waste spark system is that it is more reliable and isn’t affected by environmental conditions such as rain or dampness.

Pros – Recommended for Waste Spark Systems; Reliable
Cons – Not recommended for electronic DIS
 

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https://cartreatments.com/copper-vs-iridium-vs-platinum-vs-double-platinum-spark-plugs/

You might think that all spark plugs are the same. After all, the general purpose of a spark plug is to generate an electric current for igniting the compressed air and fuel in the combustion chamber. However, there are some differences when it comes to spark plugs. Certain ones are more efficient and perform better than others. It all depends on what type of spark plugs your vehicle’s manufacturer recommends.

All spark plugs have a central electrode and a side electrode. These electrodes were traditionally made of copper but now they are being manufactured from materials like iridium and platinum. Also, the center electrodes are being made much smaller than they used to be. This means that less voltage will be required to generate the electric current for the combustion chamber.

Overall, you will find the four main types of spark plugs are copper spark plugs, iridium spark plugs, platinum spark plugs, and double platinum spark plugs. Some have better uses than others, depending on the vehicle that you’re driving. Below you will find more details on these spark plugs and what they are good for.

Copper Spark Plugs

This spark plug is mostly made from solid copper. Its central electrode is made from nickel alloy and it has the largest diameter of all the other spark plugs. This means it’ll need more voltage to generate an electric current. Nickel alloy is a material that is soft and not very durable. This means it won’t last long. It is best to use copper spark plugs in older vehicles which didn’t have high electrical needs.

Pros – Better for older vehicles built before 1980.
Cons – They don’t last as long; Requires more voltage.

Iridium Spark Plugs

Iridium spark plugs will last the longest. Iridium is a metal that is harder and more durable than platinum. Although you will have to pay more money for iridium spark plugs, you will get what you pay for. These spark plugs have a small center electrode which means they use less voltage to generate the electric current. That is why many car manufacturers are starting to recommend iridium spark plugs for their vehicles. If you already have these spark plugs installed and you need new ones, do not downgrade to platinum or copper because they will diminish the performance of your vehicle.

Pros – Harder than platinum; Lasts the Longest; Uses Less Voltage
Cons – Expensive

Platinum Spark Plugs

A platinum spark plug is similar to a copper spark plug, except that its center electrode has a platinum disc which is welded to its tip area. The copper spark plug only has nickel alloy material in this area. As a result, the platinum spark plug is more durable and can last as many as 100,000 miles. These plugs also generate more heat, which means that debris buildup will be reduced. If you have a new car with an electronic distributor ignition system, platinum spark plugs are recommended.

Pros – Lasts longer than copper; Reduces debris buildup
Cons – Not the strongest spark plug on the market

Double Platinum Spark Plugs

If your distributor ignition system is a waste spark system, then double platinum spark plugs are recommended. This system causes the spark plugs to fire twice, once in the compression stroke’s cylinder and the other in the exhaust stroke’s cylinder. The spark for the latter gets wasted because there is no ignition there. The benefit of the waste spark system is that it is more reliable and isn’t affected by environmental conditions such as rain or dampness.

Pros – Recommended for Waste Spark Systems; Reliable
Cons – Not recommended for electronic DIS
Thanks for that info Bill. Appreciate you chiming in here with some valuable information. I think I’ll be springing for some iridium plugs here at my next service change. ?
 

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Very informative American. So I replaced my plugs recently with the manuals recommended NGK/DPR8EA-9 which apparently has a copper core. I didn't pay much attention to the differences between types of plugs. I've been getting some intermittent missing usually while accelerating. I now assume the plugs are the culprit.
 

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There is some pretty good info on plugs here. I brought this up before and I've read it more than once that plugs should be installed dry as anti-seize will give you incorrect torque ranges.
 

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There is some pretty good info on plugs here. I brought this up before and I've read it more than once that plugs should be installed dry as anti-seize will give you incorrect torque ranges.
A lot is going to depend on the material the plugs threads are made out of and the material the head is made out of so there are times when using the proper anti-seize compound is a huge benefit so that you don't end up with a galled thread and end up stripping out the threads in the head.

NGK I know coats their spark plugs with a coating that helps to prevent the threads from galling and stripping out. I am sure other brands use a coating as well but there may be some plugs that don't have a coating so always good to check the plug manufactures specs to see if they have a coating or not to prevent galling.

Very informative American. So I replaced my plugs recently with the manuals recommended NGK/DPR8EA-9 which apparently has a copper core. I didn't pay much attention to the differences between types of plugs. I've been getting some intermittent missing usually while accelerating. I now assume the plugs are the culprit.
Copper core plugs are not bad plugs they just won't last as long, in fact if you are running a high performance engine i.e. one that is built for high performance a copper core plug will provide the best performance for that application.

A stock engine does not stress the spark plug like a racing engine does, so iridium and platinum plugs can actually be a better choice because they will far out last a copper core spark plug.

As for your miss, sure you could have a bad spark plug or your might even have a bad spark plug wire, also depending on how old the motorcycle is you may even have an ignition coil starting to break down.

Also an item that most people will over look, make sure the battery terminals are tight.

You can check your spark plug wires with an ohm meter if they are showing a lot of resistance then you have a bad plug wire. The coil can be harder to track down, does the miss occur when the engine is at full operating temperature and after being run for a while, that could indicated the coil is over heating and breaking down.

I would first start off by checking the plug wires with an ohm meter and go from there as well as making sure the battery terminals are tight.
 

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Here's a quick reference to plug wire resistance.

 

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One other thing to be careful of with spark plug wires is to always remove them via the boot never pull on the spark plug wire itself, if you can use a spark plug boot pliers but sometimes due to the angle and other things in the way or just the design of the head prevents the use of a spark plug boot plier.

If could be possible that one of the ends of the spark plug wire has come loose.

Another thing to look for is the plug wire rubbing anywhere along its path, My Harley Davidson the spark plug wires rubbed the bottom of the fuel tank so I put some spiral wire harness over them and that protected the plug wire from rubbing through and allow spark to jump at the rub point which can cause a misfire.
 

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Discussion Starter #17

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As for your miss, sure you could have a bad spark plug or your might even have a bad spark plug wire, also depending on how old the motorcycle is you may even have an ignition coil starting to break down.

Also an item that most people will over look, make sure the battery terminals are tight.

You can check your spark plug wires with an ohm meter if they are showing a lot of resistance then you have a bad plug wire. The coil can be harder to track down, does the miss occur when the engine is at full operating temperature and after being run for a while, that could indicated the coil is over heating and breaking down.

I would first start off by checking the plug wires with an ohm meter and go from there as well as making sure the battery terminals are tight.
-2010 Raider with about 12K miles.
-I'll pick up an ohm meter and check the wires.
-New battery-connections are tight.
-Seems like the miss is random and infrequent. Can't quite pin down a pattern.
 
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