Split fire plug for YZ426

14 replies to this topic
  • PW50power

Posted April 02, 2006 - 10:11 PM


I have a 01 YZ 426 and I am about to change the spark plug and was wondering if anyone had ever tried a split fire spark plug in there bike. And is it really safe to run AV gas, and what do you recommend for an air filter? Thanks for all the help. :thumbsup:

  • crfmatt

Posted April 03, 2006 - 12:00 AM


It may just be me but I think the split fire is just a market gimmick. Go with an iridium spark plug. I use ngk but I'm sure there are others. For AV gas you will get mixed responses but I would just be safe and stick to unleaded. My family flys airplanes and I have started to try it but I have no expirence with it. And for a filter I would sugest a K and N. They are quite expensive i think like $50 but they are just like the ones for cars or trucks. They are very quick and easy to clean with the $7 cleaning kit and they are also claim better airflow. People have said they have to much airflow and sand and stuff can get through but I have never had a problem. There is never anything on the inside of it. Hopefully I answered some of your questions..

  • Goosedog

Posted April 03, 2006 - 04:42 AM


I agree with everything crfmatt says except for the K&N. They are sure death to dirtbikes! I've had conciderable valve wear thanks to those on more than one bike, they DO NOT filter out the fine dust. Do a seach here and you'll see how much they are despised. Go with a TwinAir filter and No-Toil filter oil. :thumbsup:

  • odlaw19

Posted April 03, 2006 - 04:52 AM


I think goosedog is right..... K&N are great for cars (i used to run one in a RB30ET - 350HP) but i agree they dont are good enough at filtering in extreme conditions.

Go for the Iridium!


  • motohess

Posted April 03, 2006 - 08:16 AM


Hey guys, the K&N filter will be the death of anything, there are lots of reports out there on thier low ability to filter dirt and they only provide better flow when they are clean, they get very restrictive when they start to get dirty. I personally wouldnt run one in my car truck or anything you want protection from dirt on. But thats just me. And yes they do flow better when new, and maybe you have not personally had any problems with the one you have been running on your truck for 54 years. All I am saying is they let me dirt through.

  • 642MX

Posted April 03, 2006 - 09:02 AM


Stay away from AV gas, Split fire plugs and K&N filters.

A stock motor doesn't need anything above premium pump gas, I personally have never seen any benefits from an iridium plug. I run the regular CR8E's in our bikes. I change them once a year and have had no problems. I use UNI filters, they seperate and are easier to get all the oil and dirt cleaned out. I use Maxima FFT filter oil, its sticky and messy, but it won't let any dirt thru it.

  • viking_in_wa

Posted April 03, 2006 - 09:47 AM


these guys are right. the avgas is a higher octane therefore burns cooler. I have used it in my bike and i am sure it runs better on premium 92 octane. as for the k&n they are junk :thumbsup: and again like everybody else go with the ngk plug. split fire plugs are CRAP.

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  • grayracer513

Posted April 03, 2006 - 10:18 AM


The idea behind Split-Fire plugs is to change the way the fuel mix is exposed to the spark by orienting the two ground electrodes so that the spark jumps horizontally (using the plug as a frame of reference). The benefit is supposed to be that the spark is more exposed to the AF mix than in the more conventional configuration, and in a very cold heat range, this may actually be true. But not with the heat range plugs typical of a YZF. The multiple electrodes are the marketing gimmick part. The spark will only cross the easiest of the two gaps at any one time unless it has a massive amount of energy dumped on the plug all at once. If you want a plug that works better than the $5 standard NGK, go with the iridiums. They'll actually deliver more spark to the combustion chamber (marginally, but it may be enough to improve starting) and they'll last longer.

AVgas is formulated for BIG bore engines, often with very long intake tracts, that run at low RPM in thin air at low temperatures. The result is a fuel that is altogether wrong for your MX 4-stroke. You don't need the extra octane at all, and you may end up with less power than you started out with, no matter what anyone tells you otherwise.

K&N filters are another thing. The original version for a YZF had media only around the sides of the element, with the "top" just a closed piece of plastic. These did not breathe well. The later version added media to the top, which solved the air flow issue.

They do in fact filter very well IF they are cleaned and oiled properly, and that is where the real trouble lies. Both foam and fabric elements like the K&N have media that is too open to the air to trap fine dust on their own, and they depend on oil to trap and hold the intruding dirt. The "squishable" nature of foam makes washing a little easier, but more importantly, makes it far easier to completely distribute the new oil throughout the entire element surface, both interior and exterior. The fabric types simply can't be squeezed and kneaded to accomplish this and depend on the penetrating ability of the oil used to spread through the entire element. Their pleated construction complicates the task further, and the result is that by far most K&N's in use today are under-oiled and not working as well as they could be. My advice is to stick with a high grade foam filter, and use a good, sticky filter oil like Maxima FFT. The filter will only work as well as you oil it.

  • grayracer513

Posted April 03, 2006 - 10:53 AM


AVgas is a higher octane therefore burns cooler.

That is incorrect. Octane measures nothing whatever except the resistance of a fuel to detonation. Nothing.

In spite of the huge weight of folk lore and other mythology to the contrary, high octane fuels DO NOT burn faster or slower, hotter or colder, produce more or less power, or ignite with any more or less difficulty than lower octane fuels. Why? Because octane does not measure any of those things; only detonation resistance. It is entirely possible that any particular higher octane fuel might perform better or worse in your engine than a lower octane fuel, but that would be a result of the chemistry used to raise the octane rating, and not the rating itself.

This post and/or This one

Then Read This Thread for a good discussion of the subject, and then for the complete story in plain English, read:

Octane Numbers by Bruce Hamilton.

  • crfmatt

Posted April 03, 2006 - 03:24 PM


Hmmm... sounds to me as though I may want to go back to a regular filter. Even though I have been fine with mine I guess it might not be as good as I thought. :thumbsup:

  • Goosedog

Posted April 03, 2006 - 04:06 PM


Hmmm... sounds to me as though I may want to go back to a regular filter. Even though I have been fine with mine I guess it might not be as good as I thought. :thumbsup:

You won't know how bad it's been until they tell you the titanium coating on your valves is gone. :thumbsup:

  • David37

Posted April 03, 2006 - 09:38 PM


Stay away from the AV gas and just use premium unleaded. IMO I wouldn't use a K&N filter due to the lack of filtration, buy yourself a Twinair or Uni air filter. I use No Toil on my air filters.

  • 2fastwhitey

Posted April 04, 2006 - 07:13 PM


Like everybody else said go with a foam filter and a good oil like uni or something. I have a 426 too and I run the Iridium plug for the few extra bucks.(CR8EIX) Haven't had any problems with this plug, no real noticable difference, but its cool to think that iridium is found primarily in meteorites.

  • jocolo

Posted April 04, 2006 - 07:27 PM


AV gas even 100LL (low led) blue or 100 green is design to run a high altitudes and constant RPMs

  • mpl239

Posted April 04, 2006 - 07:45 PM


With the stated 12.5:1 compression, I run 100 low lead av gas. No issues no detonation. But as in the airplane, avgas burns white on the exhaust. This does not make it lean. Check the inside of the plug to confirm your mixture.

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