Motorcycle Forums » Harley Davidson

New Harley Davidson Screaming Eagle Spark Plugs

    • 835 posts
    September 15, 2009 8:36 AM PDT
    Has anyone used the newest HD Screaming Eagle spark plugs.  I went to buy new plugs at my local dealer the other day and they recommended these new plugs.  The main thing I noticed about them is the center electrode is a tiny piece of wire, instead of the normal 10mm or so electrode we are used to.

    Since I had not heard anything about them, and I was getting ready for a long trip, I opted to stick with the tried and true original H-D replacement plugs.

    Just curious if anyone has used these and has an opinion on them.
    • 5418 posts
    September 16, 2009 3:40 AM PDT
    Actually just put those in my Road King on the last spark plug change. Like you my Harley dealer recommended them so I figured what the heck.

    So far I haven't noticed any difference in performance, it's been about 2,000 miles...mostly around town, and one long run. My bike is a stock 2007 Road King, except for the air cleaner and exhaust... running the SuperTrap slip-ons. I am very curious to see how well they hold up. That fine little center electrode doesn't look all that tough to me, but we'll see.
    • 19 posts
    September 16, 2009 4:41 AM PDT
    24,000 miles on my 1800vtx and ain't got around to changeing them,you mean you have to change them? well i do change my oil every a,a,a, year, i was told, if it ain't broke,don't fix it? those tires wear fast though,,no more burn outs for me!!!
  • November 4, 2009 3:11 AM PST
    Screaming Eagle Spark Plugs will not make MC Scream

    Why Spark Plugs Need To Be Replaced

    One of the leading causes of hard starting is fouled or worn spark plugs. When a fuel injected engine that normally starts quite easily has to be coaxed to life, it often means the spark plugs are overdue for a change. As the electrodes wear, the voltage required to jump the gap and ignite the fuel mixture goes up. At the same time, accumulated deposits on the insulator can drain off voltage before it even has a chance to form a spark. So the engine fails to start or starts only reluctantly after prolonged cranking.

    One of the reasons why spark plug sales take off when cold weather arrives is because many motorists put off changing the plugs until they absolutely have to. The spark plugs continue to rack up mile after mile until they have deteriorated to the point where they are causing noticeable starting and driveability problems.

    Emission checks will catch a lot of bad spark plugs and force motorists to change plugs that need to be replaced. But in areas where emission checks are not required, the only incentives for changing the spark plugs are the driveability problems created by the plugs themselves. So many motorists today think they are saving money on maintenance by putting off a spark plug change until it is obvious the engine needs new spark plugs. Then and only then will they begrudgingly spend any money on a new set of spark plugs.


    What motorists need to know is that spark plugs do NOT last forever, even the long-life 100,000 mile plugs. All spark plugs need to be changed sooner or later. Here's why:

    REASON #1: New plugs maintain peak engine performance and efficiency. Every engine will misfire occasionally. But as the number of misfires per mile goes up over time, it increases exhaust emissions, wastes gas and reduces power. In the past, most motorist would not notice the gradual decline in ignition performance until it reached a point where it created a steady miss, caused the engine to run rough, buck or stall, or made it hard to start. Not so today. All 1996 and newer vehicles have an OBD II onboard diagnostic system that tracks ignition misfires. When the rate of misfires exceeds a certain limit and causes emissions to increase 50% over baseline levels, it illuminates a warning light. Too bad older vehicle do not have this watchdog system. So on older vehicles, replacing the spark plugs at the recommended service intervals for preventive maintenance will reduce the risk of misfires and maintain peak engine performance. For standard spark plugs, the service interval is typically every 45,000 miles. For platinum spark plugs, it is 100,000 miles.

    A new set of plugs is not a cure-all for driveability and emissions problems, but in many cases a plug change can make a significant improvement. Changing the plugs can reduce hydrocarbon (HC) emissions up to several hundred parts per million, which may make the difference between failing and passing an emissions test.

    REASON #2: New plugs improve cold starting. Bad plugs are often responsible for many cold weather "no start" service calls. Many times the battery has been run dead while cranking the engine because the plugs would not light the fire. When the old plugs are removed and examined, they are often found to be worn or dirty. New plugs reduce the voltage requirements on the ignition system, which decreases the chance of misfire while leaving more amps for the starter and injectors.

    Wet fouled plugs can also prevent an engine from starting, but in many instances the fouling problem has nothing to do with plug wear or neglect. If an engine is flooded with fuel while it is being cranked, gasoline can soak the plugs and bleed off the ignition voltage before it forms a spark. Wet fouling tends to be more common on older vehicles that have carburetors because pumping the gas pedal can easily flood the engine with too much fuel. Flooding can also occur if the choke sticks, the float is set too high or the needle valve leaks. On fuel injected engines, wet fouling is less of a problem but can happen if a cold start injector leaks or there is a fuel calibration problem that creates an overly rich startup mixture. The cure in all cases is to wait for the plugs to dry out, or to remove the plugs and clean or replace them.

    REASON #3: New plugs minimize the risk of catalytic converter failure. A single misfiring plug can dump enough raw fuel into the exhaust to overheat and damage the converter. The presence of higher than normal quantities of unburned gasoline in the exhaust will cause the operating temperature of the converter to soar, which may lead to a partial of complete meltdown of the converter substrate. This, in turn, may form a partial restriction or complete blockage in the exhaust that creates enormous backpressure and chokes off the engines ability to exhale. The engine may lack power, especially at higher speeds, and deliver terrible fuel economy. Or, it may stall and refuse to run after it is first started. Replacing the converter will solve the restriction problem. But unless the spark plugs are replaced, the new converter may soon die from the same ailment.


    The spark plugs are the business end of the ignition system. Whether an engine has a conventional distributor or a direct ignition (distributorless) system, a good set of plugs is absolutely essential for peak performance.

    The typical spark plug needs anywhere from 5,000 to 25,000 volts from the ignition coil before it will fire. The exact firing voltage depends on:

    Plug gap The wider the gap, the higher the voltage required. The gap must be set to specs for good ignition performance.
    Electrode condition Wear increase voltage requirements.
    Fouled electrodes may not fire at all!

    Engine load Higher load increases voltage needed. If the plugs are worn or gapped to wide, they may misfire under load.
    Resistance Electrical resistance in the plugs and wires increases voltage required. Replacing worn, damaged or loose fitting plug wires is recommended for improving ignition reliability.
    Operating temperature A cold plug requires more voltage to fire than a hot one.
    Reliable ignition, therefore, requires a hot spark from the coil, good plug wires to carry the juice, and spark plugs that are clean, in good condition and gapped properly. If any of these criteria are not met, the spark may not reach it intended destination causing the engine to misfire.

    One way to tell if the plugs need changing is to look at a vehicle's odometer. If it has been more than the recommended number of miles (usually 30,000) since the spark plugs were last changed, it is time for a new set.

    Another way to tell is to observe the secondary ignition pattern on an oscilloscope. If there is an open plug or wire, the plug will not fire causing the firing voltage to shoot up to the maximum output of the coil. Badly worn plugs or plugs that have been misgapped too wide will also increase the firing voltage dramatically (as can a bad rotor and/or ignition cables with excessive resistance). If the required voltage exceeds the maximum output of the system, the plugs may not fire. If the pattern shows initial secondary spikes approaching the upper voltage limits of the system, therefore, it is a sure sign that the plugs (and/or cap, rotor and cables) need attention.

    A fouled plug (or shored ignition cable), on the other hand, will show an unusually low firing voltage.

    Firing voltages should not vary by more than 3 kV cylinder to cylinder. A cylinder that shows an abnormally low firing voltage probably has a grounded spark plug (deposits bridging the electrode gap), or a shorted ignition cable. A cylinder that shows an abnormally high firing voltage compared to the others likely has an open ignition cable or a plug with a wide gap.

    The plug firing time (spark firing line) portion of the secondary ignition display shows the duration of the spark in milliseconds (thousandths of a second). The average spark duration with the engine idling should be about 1.5 milliseconds.

    A duration of less than 0.8 milliseconds would mean there either is not enough voltage to keep the spark going (low coil output), or the voltage is having trouble reaching its destination (excessive resistance in the plug wires).

    A longer than normal spark (1.8 milliseconds or more) is an indication that the firing voltage is experiencing little resistance because a plug is fouled or grounded (or a plug wire is shorted) probably due to accumulated carbon deposits. Fouling can be a problem if a plug's heat range is too cold for the application (which can be solved by installing hotter plugs). But it may also be the result of excessive oil consumption due to worn valve guides or seals, worn rings, or even short trip stop-and-go driving.

    Intermittent misfires can be caused by a variety of ignition, fuel or mechanical problems. Lean misfire occurs when there is too much air and not enough fuel, so the engine should be checked for air or vacuum leaks, dirty injectors, carburetion problems or a leaky EGR valve. If the misfire appears to "jump around" from cylinder to cylinder, a manifold vacuum leak or a leaky EGR valve may be the cause. But if the misfire is isolated to a single cylinder, a worn or fouled spark plug (or bad plug wire) is the most likely cause.


    Click on image at left to view Spark Plug Diagnosis Chart.

    Examining the tips of the spark plugs as they are removed can reveal a great deal about the health and performance of an engine. The appearance and color of the deposits can reveal other problems that may need fixing:

    Normal deposits Light brown or tan colored.
    Fuel fouled spark plug Black fluffy carbon deposits indicate an overly rich fuel mixture or possibly a weak spark. Check for such things as a stuck choke, a heavy or misadjusted carburetor float, a leaky needle valve in the carburetor, leaky injectors, low coil output or high resistance in the plug wires.
    Wet spark plug A wet spark plug means the plug has not been firing. If not due to engine flooding, the problem may be a bad ignition cable (excessive resistance, shorted or arcing). But wet fouling can also be caused by dirt or moisture on the outside of the plug that provides a conductive path to ground, or by an internal crack in the ceramic insulator that shorts the plug to ground.
    Oil fouled spark plug Heavy black deposits with an oily appearance. These are the result of oil entering in the combustion chamber, probably past worn valve guides, guide seals or rings. Switching to a hotter plug may help prolong plug life somewhat, but no spark plug will survive long under such conditions. The only permanent cure to this condition is to fix the oil consumption problem.
    Glazed spark plug Yellowish melted appearing deposits on the insulator tip that result from high temperature operation. The engine may be running too hot (check for cooling problems), the EGR valve may be inoperative and/or the heat range of the plug may be too hot for the application. Switching to a cooler plug may be necessary if no other problems are found.
    Damaged plug If the electrodes have been smashed flat or broken, somebody put the wrong plug in the engine. A plug that protrudes too far into the combustion chamber may hit the piston or a valve. Always follow the plug manufacturers application recommendations when selecting replacement plugs to prevent this kind of problem.
    Overheating If the spark plug insulator is blistered, white and free from deposits, something is making the plug run too hot. If the heat range is not too hot for the application, check for cooling problems, incorrect ignition timing or a lean fuel mixture.
    Melted electrode A symptom of severe preignition. The spark plug has been running too hot for a long time (see overheating above). This can be very damaging and may burn a hole through the top of a piston!
    Detonation If the insulator is split or chipped, detonation (spark knock) may be occurring in the engine. The underlying cause here might be an inoperative EGR valve, overadvanced ignition timing, excessive compression due to accumulated deposits in the combustion chamber, or engine overheating.


    When spark plugs are replaced, you might want to upgrade to a premium long-life platinum or iridium plug. These plugs cost a little more initially, but can actually save you money in the long run because they do not have to be replaced as often. Many of these plugs can go 100,000 miles or more. Such plugs would be a good choice for any vehicle where access to the spark plugs is a problem.

    Another option is upgrading to "performance" spark plugs. These plugs typically have unique electrode configurations that increase spark exposure to the air/fuel mixture and have multiple edges to reduce the chance of misfire. Performance spark plugs are usually more expensive than standard or even long-life plugs, but may be a good alternative if you want the ultimate in ignition performance.

    There are also spark plugs today that are specially designed for truck engines. Such plugs have increased fouling resistance and oversized electrodes for longer service life.

  • November 4, 2009 7:13 PM PST
    laborer wrote...
    24,000 miles on my 1800vtx and ain't got around to changeing them,you mean you have to change them? well i do change my oil every a,a,a, year, i was told, if it ain't broke,don't fix it? those tires wear fast though,,no more burn outs for me!!!

    and if you're not careful your overhead cams and valve train will live to regret that... all motorcycles no matter who the company is requires that owners be smart and diligent with upkeep, thankfully now though the MoCos got smart and built tougher bikes. We could have the lastest and greatest most advanced speed machines on the market but since most owners are either too cheap, too lazy or just too prideful do do the necessary upkeep we get stuck with the same ol' same ol' from the factories.
    • 18 posts
    November 6, 2009 4:47 AM PST
    Just put the new SE plugs in last weekend. I'll let you know how it goes.
  • November 9, 2009 1:17 AM PST
    the new SE plug... and I've talked to other techs who all seem to say the same thing... wow a $16.00 set of spark plugs... who'da thunk it?
    • 5418 posts
    November 20, 2009 2:43 AM PST
    Black9 wrote...
    the new SE plug... and I've talked to other techs who all seem to say the same thing... wow a $16.00 set of spark plugs... who'da thunk it?

    Got to agree...I tried them and now have about 3,500 miles on them.  Didn't notice a bit of difference.  Back to the stock plugs for me.

    • 1042 posts
    November 21, 2009 1:01 PM PST
    Used stock harley, the new SE, and now I have a set of NGK's from Advance Auto Parts that I think cost about $2 each and they got 1200 miles on them with nary an issue. Couldn't tell ya the difference between any of em except about 12-14 dollars.
  • November 21, 2009 2:22 PM PST
    Ran Champions in the Shovels and Evos forever. they work fine and don't cost an arm and a leg. Did you ever notice that when the factory (Harley, ford, Chevrolet, etc) puts their name on something that they RECOMMEND it for use in their vehicle but it costs 2-12 times what a normal part costs?
  • November 21, 2009 8:58 PM PST
    I run NGK's in the 69. With it being a kick start only the spark is very important and they seem to work the best for me plus I am cheep as hell
  • January 10, 2010 2:35 AM PST
    I use NGK Iridiums with good results on my Electra and Sportster both .. about $7.00 each may be a bit of overkill but they have been winners for me for almost 5 years now on every bike used them on ..
    • Moderator
    • 1362 posts
    January 12, 2010 4:38 AM PST
    Ran Screaming Eagle, Tried NGK....... Best plug I found........ Autolite... Yip autolite gapped @.039
  • January 15, 2010 1:28 AM PST
    I wish Halo would make some for the hogs. I put them in the 6-cyl. car and gained a couple mpg plus a tiny bit of power. I doubt Harley will approve of anything hotter than stock for obvious reasons, so spark formation is the only other venue possible, IMO.
    • 5418 posts
    January 15, 2010 2:03 AM PST
    Just checked those new style HD Screaming Eagle plugs I put in about 6 months ago. They have about 10,000 miles on them and still looking pretty good, probably about the same as any plug would look at this point. Like I said earlier, I noticed no difference at all in performance. Going back to standard plugs on the next change...don't see any additional value for the extra cost.
    • 844 posts
    February 27, 2010 5:00 PM PST
    highrisk wrote...
    Ran Screaming Eagle, Tried NGK....... Best plug I found........ Autolite... Yip autolite gapped @.039

    Have to give them a try.  I usually run the stock plugs from the dealer..

  • February 27, 2010 10:06 PM PST
    If your plugs don't last an easy 20000 miles,
    1. you drive like a fuddy duddy.
    2. you buy regular fuel.
    3. your coil sucks.
    4. you have the wrong plugs, wrong length or heat range.
    • 1 posts
    March 3, 2010 11:49 AM PST
    Flatlander, your plugs may well "last" 20k if you take care of them, only if you consider lasting to be that they still look good. It has been my experience after years of wrenching on bikes, that a plug - any plug - is spent after 10-15k (depending on how you ride. I have changed many of plugs that looked fine and the HP and mileage went up with the new plugs.

    We are talking 5 or 6 bucks and ten minutes of work...get them damn things out of there long before 20k.
  • July 20, 2010 11:33 AM PDT
    I change my plugs every 10,000 miles whether they need it or not...just like every year I buy a new battery whether I need it or not... batteries and plugs are easier to change and cheaper than a fried stator:-)
  • July 20, 2010 1:01 PM PDT
    Love this post!! Thank you for bringing it back from the dead post pile. Simple stuff for me that I can be knowledgeable about and do!!... that works.
  • March 8, 2011 7:56 AM PST
    GNK are much better plug :)