Plug reading 101

Discussion in 'Technical Posts' started by imlostagain, May 18, 2002.

  1. imlostagain

    imlostagain Rookie DRN Member

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    Need jetting help FAST !!!!



    Ok , I have run into a problem with jetting my CR 144. I just installed a 1368 needle( Mr.Gorr's reccommendation) and reset my V-Force reed tension to the low setting .My problem is that I do not have a main jet large enough to get a good plug reading.I currently have a 180 main installed and the bike runs excellent through the whole range. I can ride aggressively for like 20 minutes and pull the plug it looks perfectly tan but not when doing a WOT plug chop(plug will be white ) I plan on going to a local race in the morning and am wondering if I can get away with running a richer ratio like 40:1 (currently 36:1). Would I risk engine damage ? Or will that even be enough to make a differance??If I recall Eric Gorr had suggested going to a 162-165 main so why Am I needing to go so large on the main Thanks again for ANY help on such a short notice.....
  2. crkid

    crkid Subscriber

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    first, going from 36:1 to 40:1 would be running leaner, not richer. i take it you're racing MX, so you will be at high rpms much of the time. running it leaner would not be good for the engine. going to say 32:1 ratio may not make a difference, except the plug may foul sooner. but if you are a person that keeps the bike revved out, then that could be your best bet until you can really get in and tinker with it. sorry for poor info, but it's the best i can do with what i got.
  3. Rich Rohrich

    Rich Rohrich BioHazard

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    Changing the ratio from 36:1 to 40:1 would put more fuel into the chamber, but regardless it's unlikely to help the situation.

    Within the framework of the limited info you provided it sounds like the plug you are running may be a bit warm for WOT operation on your setup, or you aren't reading the plug in the correct area. Remember you can't read the main jet from the nose of the sparkplug insulator.
    Last edited: Feb 12, 2008
  4. imlostagain

    imlostagain Rookie DRN Member

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    I have been using a NGK BR9EG .Should I try the BR10EG?
    I may not have access to the "EG" plugs in the morning but should be able to get the "ES" . Might that suffice for the day. Thanks .....
  5. Rich Rohrich

    Rich Rohrich BioHazard

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    NO, if you are running a 9 then the plug heat range is not the issue. Reading plugs isn't a simple task so if your bike runs strong at WOT and it isn't knocking or pinging or overheating. Then fill up the tank and ride it.
  6. imlostagain

    imlostagain Rookie DRN Member

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    As for reading the plug...... I believe I understand where to look ( inside the plug on the ceramic)and the plug does show a nice tan color under general riding. To be honest I'm not entirely certain what a lean plug looks like . I am under the impression it is lean simply due to absence of coloring on the insulator but the electrode is clearly white during a WOT plug chop in 5th gear for 20-30 seconds . The motor was warmed up and I was riding in a slightly inclined field. Am I correct??
  7. Rich Rohrich

    Rich Rohrich BioHazard

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    See the black ring at the bottom of the ceramic? That's where you have to look to read the mainjet. All you are reading higher up is the plug temperature. In the case of the pictured plug the heat range is a little too cold and could probabaly go up a step on the heat range and the mainjet is pretty close to perfect. It could go a step leaner on the mainjet without any problems.

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  8. imlostagain

    imlostagain Rookie DRN Member

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    OK Rich, Upon further inspection the plug does have a "slight" tan coloration further down into the plug. Can I assume the 20-30 second ride wasn't enough to get more than a "slight" tan or should I try another size richer? Is there reason for concern with the white on the electrode after a WOT plug chop ? Thanks for the great example.....All this time I was looking about a 1/4 of the way into the plug. Would the fact that my insulator is tan after a day of riding indicate the overall jetting is relatively close or does it primarily diagnose 3/4 and up throttle positions?
  9. Rich Rohrich

    Rich Rohrich BioHazard

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    That portion of the plug doesn't tell you anything about the mainjet or anything else about the jetting other than how the current jetting influences the relative plug temperature.

    If you can't see down to the ring at the base of the insulator (see the picture) then you aren't reading anything relevant in terms of the mainjet strength PERIOD. You can't "read" the pilot or needle setting on the plug regardless of what people tell you, so don't waste your time.

    Running the engine WOT for 20 to 30 seconds under a load (like sligthly uphill) should be enough time to produce the mixture ring at the base of the insulator but whether or not it will produce noticeable color at the nose (top) of the insulator will depend on the oil type, oil volume and the fuel you are running.
  10. Jaybird

    Jaybird Apprentice Goon

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    imlost, use a flashlight to look down at the base of the insulator. Almost impossible to do in regular light...or without a nice lathe. :)
  11. Rich Rohrich

    Rich Rohrich BioHazard

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    I guess I should have made this clearer. Jaybird is right, you can't see the fuel ring with the naked eye when the shell is still attached to the plug. You need a light and some kind of magnifier to see down in there where the metal plug shell and the insulator meet.

    The standard Champion plug viewer looks like the picture below, Childs & Albert sells a newer style viewer with two lenses 5X and 10X. I have both and the newer C&A version is far superior. It costs about $65 but that's cheap in the long run ;)

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  12. bscottr

    bscottr Lifetime Sponsor

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    Rich,
    Excellent thread. This one should be renamed "How to read a plug.....properly!"

    Thanks,
    Scott
  13. Rich Rohrich

    Rich Rohrich BioHazard

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    As long as we've started down this torturous road once again :) we might as well do it right and take the discussion to the next level.

    It's important to understand the significance of the rider, the track, the fuel etc when attempting to read a plug. The same engine with the same jetting can have plugs that look radically different when you change the load or the amount of heat going through the plug. This is one of those areas where explaining it doesn't provide enough information so showing clear pictures hopefully will help further everyone's understanding of the subject. Below are four pictures of plugs 2 pictures as complete plugs and the same plugs with the shell removed. These were pulled from my 2001 CR125 at DW01. One plug was a BR8ES one was a BR9EVX.

    I won't tell you anything more till later. Draw your own conclusions.
    Take a look at the pictures and think hard about what you are seeing. We'll pick up the discussion after you guys get a chance to check out the pics. Have fun.


    We'll start with the BR9EVX with the shell removed.

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    Last edited: Feb 12, 2008
  14. Rich Rohrich

    Rich Rohrich BioHazard

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    BR9EVX with the shell

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  15. Rich Rohrich

    Rich Rohrich BioHazard

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    BR8ES with the shell removed.

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  16. Rich Rohrich

    Rich Rohrich BioHazard

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    BR8ES with the shell

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  17. Rich Rohrich

    Rich Rohrich BioHazard

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    another view of the BR9EVX

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  18. Rich Rohrich

    Rich Rohrich BioHazard

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    and another view of the BR8ES

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  19. SFO

    SFO Lifetime Sponsor

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    Are you running the same fuel in all of these plug pictures?
  20. Rich Rohrich

    Rich Rohrich BioHazard

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    Same fuel & oil.

    Don't let the yellow tint on the BR9EVX shell pics confuse you. The actual color is closer to white (see the cutaway shot) , it's just hard to white balance this type of shot and still show the correct details on the threads and the flat of the shell.
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