What size Plug gap do you run ?

When I had my big Jeep truck, I put in a new Jacobs ignition system that had a very high voltage coil in comparison to the stock. The instructions told me to open the gap .02 LARGER than recommended. When I did so my power went up drastically and my gas millage went from 9.5MPG to 13.8MPG. Since then I have been running a larger gap on everything with a high performance coil. On my GPZ with Dyna 2.2Ohm coils I opened my gap to .045" from the recommended .030 It seams to make quite a bit of difference and I have no spark blowout at high RPM.

It all hinges on whether or not a "bigger" spark will somehow create a significant or even measurable performance increase. That would be true if and only if the stock ignition's 25 - 30 kV open circuit capability was somehow inadequate to fully ignite the fuel mix. I tend to be very skeptical for the obvious reason:

If there was any extra power to be had with a higher spark voltage jumping a bigger gap, the bike maker's would have scooped it up and designed it into the bike. It's actually quite easy to get more voltage out of the ignition system as evidenced by aftermarket devices.


I have an aftermarket CDI on mine which supposedly can put out about 60kV open circuit voltage with a stock coil. I run my gaps at about .035".

On my old 1977 Kz1000, I installed a then hot ignition system called "Gerex". I believe the plug gap was opened up to 0.045" or 0.060".

I also wondered about this Otakar.i have a dyna2000, and 2.2 coils. the instructions didnt say to change the gap so i did not. i have not had any issue, or detonation. it does make sense that the new coils would be capable of jumping a larger gap, i just had no way of telling how much or if there would be any dif .
the old bikes had barley adequate ignitions to start with. add age , and HP, and u have a lack of spark . did u experience spark blow out? how could u tell? did it miss at higher rpm's?
what is the stock spark advance for a gpz, with a bathtub head, and a round chamber? are they the same?

I used to get spark blow out on my first Z1R all the time. Once I got to about 125-130mph the engine would just shut down. That could be catastrophic (as it was)when you have to pull the clutch in, and hold it at that speed. There is no way that you can put the bike into neutral. By the time I came to a stop the clutch pusher rod friction welded itself to the pusher plate and than to the adjuster screw face. At that point it spun the screw all the way in and blew out the case. I than replaced the ignition with the "Martek" infrared ignition (the best ignition ever made). The bike did the same thing. This time I just left it in gear with clutch engaged and coasted to a stop. At that point I bought the "Martek" "Blue Goose" coils which wer rated at 80K volts. I opened the gap to .040 from the .030 stock. I never had spark blowout again. I called "Dyna" the other day and asked them what gap the coils will handle without putting too much load mack on the ignition (stock Kawasaki IC ignition box with 2.2 Ohm Gray coils) I was told that even .060 would be safe. I have been running
.040 all last year and it ran great It seamed that I had better power but I definitely had better fuel millage with the larger gap. I will now open the gap to .045 (1.15mm) and leave it there. This trick works the best with a "U" groove spark plug like the Denso W24ES-ZU or the Accel #0142.

That's good to know. Thanks for the info . I'll bump mine up too. how are u going to tell if there is an improvement at .45 or more?. how do u know it works better with the U groove plugs? I was thinking that if i am ever satisfied with my jetting, that i would change to an Iridium plug. I thought they were supposed to be the best right now?

That is a gimmick. Those plugs are great if you expect them to last you 100,000Mi+ For our use Silver plugs are actually the best. They give the best spark because silver is actually the best conductor (yes it is better than gold or platinum)the other two are used in electronics because they do not corrode which silver dose. The reason the U grove works so well, well I'll just give you a link that explains it better than I can.

go.mrgasket.com/pdf/sparkplugs/What_Is_A_U_Groove.pdf

But if you like Iridium than here you go.

www.densoiridium.com/

It seems that u can get both in 1 plug. this is a quote from the Denso Q&A page.
. What makes Iridium better?
A. Until recently, platinum was considered the best material to use on the top of an electrode because of its durability. However, Iridium is 6 times harder, 8 times stronger, and has a melting point 1200 degrees higher than platinum. Put that into a harsh environment such as an engine piston chamber, and you have a spark plug that can resist wear much better than platinum. Additionally, the DENSO Iridium Power alloy is so durable; it allowed our engineers to produce the world’s smallest center electrode (.4mm) which reduces the voltage requirements, concentrating its sparking power. Also, its smaller size, combined with the tapered U-Groove ground electrode, allows more room for the flame kernel to develop and produce a more efficient combustion.

My 2001 GMC truck came with Iridium plugs from the factory. I just changed them at 150,000 kilometors.(93,000miles) and they still looked good.
They are pricey though.about $12 each.But u buy them once for your bike and you are done.Plus the thinner wire is supposed to be better for spark(less voltage required)

If you are running aftermarket coils than much of that lingo is irrelevant. As you said they last forever in an ideal environment. The problem is that our bikes burn a lot of oil. This means that the plugs carbon up. This requires changing them every once in a while. This is why when Denso switched to the SMALL Iridium plugs from the platinum ons I bought what I could find in the Platinum. The U grove is larger and in our High RPM situation they are better. The only three plugs I use are the Denso W24ES-U the Beru Silverstone S7 and Acell 142. Those have given me the best results.

otakar wrote:

The only three plugs I use are the Denso W24ES-ZU the Beru Silverstone S7 and Acell 142. Those have given me the best results.

So are these all Platinum, U groves, just dif manufactures?
Which ones replace the NKG B8ES ?

All three of these are equivalent to the B8ES the two that are U grooved are the Denso and Acell. The Beru is not, that is just a silver core plug that has a wider heat range.