Who's got the 411 on YZF plug reading?

13 replies to this topic
  • RichB

Posted March 28, 2002 - 05:54 AM


I'm real curious about the inside rim of the plug specifically, if you can tell anything by looking at it as opposed to just reading the insulator and tip/pipe?

If the insulator is bone white, the electode slight grey to bare, but the inside rim (metal portion) is black what does that indicate?

I just richened my needle back to the stock position and it doesn't seem to be running as clean as when I had the needle 1 step leaner however, I get the above plug reading which makes me think I'm too rich in one area and maybe lean in another.

Oh, the reading on my pipe (outer tip and inside the throat of the slip on is greyish.


  • John_Lorenz

Posted March 28, 2002 - 06:24 AM


You asked:
If the insulator is bone white, the electode slight grey to bare, but the inside rim (metal portion) is black what does that indicate?

Without seeing the Plug First hand and some other factors i.e. Was the Bike @ runnig temp ?, When did you shut Motor Down, AKA Fast Straight, Idle or ?

But it looks like you are a bit leen at bottom Mid may be rich and top is runnig about right ? Her is Why !! :)
1: If the insulator is bone white,the electode slight grey to bare, Answer- Bottom to Mid Lean SHould be looking like a SoCal Blond with a good Tan
2: but the inside rim (metal portion) is black
Answer TOP Range is FAT little rich should be as I stated above TAN / Brownish. Is the black flacky like soot ?

What Pilot ?
What Needle Position
What Main ?

  • RichB

Posted March 28, 2002 - 06:38 AM



I put a fresh plug in and run it at practice for about 2 hours of riding. I pulled the plug after I got home so I did put back off the track for about 2 minutes to my truck.

The black could be flaky if I put some more time on the thing.

So you're saying that the metal portion is an indicator of needle setting, electrode is top end and insulator is bottom to mid (pilot/screw).

I like what you're saying except the bike ran better when I leaned out the screw to 3/4 out instead of the 1.5 out I started with. Maybe it's because I riched the needle too much so I had to compensate for the rich needle setting by leaning out the screw position effectively leaning it out in the crossover area between the screw/pilot to need area of the jet range?

Thanks again!

  • John_Lorenz

Posted March 28, 2002 - 07:03 AM



Bingo, What Pilot are you running ?, if you are running the pilot Screw in this means it is cutting off Air to the pilot effectivly Fattening the Mid Up by the Needle. Sounds like your chasing your tail :)
Here is what I would do:
1: Place a 45 Pilot If you havnt already
2: Back the Pil Scr out 1.5 - 1.75
3: Set the Needle Back to Stock Position

These Beast are way lean at bottom, you can go crazy trying to match the ranges. Next time you get off the track before you shut down to your truck, Ring it through the Gears WFO style, Shut the Bike Down by Pulling in the Clutch Hit The Kill B and coast to the truck.
The Yank that Plug.

Good luck

  • RichB

Posted March 28, 2002 - 11:19 AM



I'm running stock jetting all around i.e. 42, middle clip, 162 main.

  • RichB

Posted March 28, 2002 - 11:58 AM


Sorry but I should say that it has always run a heck of a lot better with 1 or even 2 clip positions leaner than the stock 4th position. That said, should I still try a 45 pilot with a needle set 1 leaner? That's what I'm fighting with myself.

  • John_Lorenz

Posted March 28, 2002 - 12:06 PM



Ya Most definetly, I would also just pickup a 165 and 168 main, throw the 168 in first. But definetly stick the 45 Pilot in then drop the clip down 1 from stock.

Set you pilot screw out 1.50 to start then adjust out accourdingly.

No more then 2.0 turns. We all know how them bastards will fall out.

Have you done the BKmod Yet ?

I wil try and get a post of me Plug off my bike for refreance

[ March 28, 2002: Message edited by: EgoAhole ]

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  • 2_SMOKE

Posted March 28, 2002 - 02:17 PM


Its hard to get these 426s dialed in why to many problems,thats why I switched to the number 1 bike made 2002 cr 250 This bike will win the supercross until they go to 4 strokes then the crf will take it,your bikes are way to heavy for motocross unless your sponsored and they pay to make it 20lbs lighter.Sorry guys its just the facts.

  • Boit

Posted March 28, 2002 - 02:28 PM


If you really want to get into the science of reading a spark plug, you will need to slice the plug open on a band saw or similar machine. This info can be found by researching the web.

2 smoke. Those aren't facts. That's just the musing of a fool.

  • HondaMan

Posted March 28, 2002 - 03:37 PM


I had yzf426 too, and I agree with 2 Smoke, they
are too heavy for motocross. Seems like everyday
there is something else to fix or adjust on

  • RichB

Posted March 28, 2002 - 03:51 PM



No I haven't done the BK yet mainly because all and the bike is running very well (except when I went to the richer stock setup this week).

I just got to tinkering with the jetting because I hardly ever see anyone post that they are running the needle LEANER than stock. For some dumb reason mine likes the needle 1 clip leaner this time of year and 2 clips leaner in the summer here (100+ degress).

I dug a 6/32 tap out today, all I need to do is go buy a couple of springs and a screw at home depot. I already have Garrett's pages printed out. I guess I should give it a try even though I don't get the hesitation when I ride like some folks do.


P.S. I'm still trying to figure out how my lap times are better then when I had my 2 smokes if I ride a heavy bike. Also, I haven't had 1 mechanical problem with this thing. The only gripes I have is stuff I tinkered with in search of some greater utopia.


  • 2_SMOKE

Posted March 28, 2002 - 06:39 PM


Is that for your first lap or through the whole moto.They beat you up after the first 3 laps just face it they are tanks.

  • grashoper250

Posted March 28, 2002 - 08:44 PM


Yes, they are tanks, especially if you are a little twig legged weakling.

  • Boit

Posted March 28, 2002 - 09:44 PM


What was I thinking? Of course Honda is FAR superior to Yamaha. Satisfied? Chevy is above a Ford.....Sony is better than JVC...Joy is better than Dawn........etc.

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