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Discussion Starter #1
How do you guys take a plug reading?  I am trying to pick the right main jets for my 99 ZRT800, but I can't seem to get a good reading.

I'm installing new plugs, then going for a 1000' wide open blast, then hitting the kill switch as I take my thumb off the throttle.  I don't get any color on the center insulator that way.  Should I bee looking down the hole at the piston?

Thanks for any help,
Scott

PS  I running 390s with a Power Breather and a D&D silencer at 30 degrees and 500 feet when I'm checking the readings...
 

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It depends on what plugs you are running.  If you are using the NGK BR9EYA's then you should be looking at the center electrode. There will be a silver/grey color on the tip. How far the color goes down the electrode determins how lean you are getting. You want this color to be at a slight angle down the electrode. The A/C performance manual has a really good section on how to read plugs. They have a diagram of what I just described. Your dealer should be able to get one for you for about $30.  You may still be able to get the 1999 version.
 

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Don't let go of the throttle until you stop.  The plug should be brown and a nice white crown around the tip of the electrode.  the further down the white crown goes the leaner the sled is.  Also the piece of metal the bends over the electrode.  You shold see black/brown color about halfway up to the top.  This would be a good plug.
 

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Discussion Starter #5
I am running BR9EYA plugs, but I am not getting any color at all in 1000 feet.  I feel that I should be plaenty rich with 390s.  How far should I have to run it to get a good reading?
 

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Try just running it normal for a while to get it good and warm. Then do your blast. You need to get a little color on those plugs. Its difficult with new ones. If your only messin with mains it won't hurt to run for a while in the half throttle area.
 

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Here's another tip. Once you've done this a few times. you can tell if you have a lean or rich condition just by the feel from bog to hesitation. They also say that plug reading is not the actuall best way to tell if you are too lean or rich. They say the best way to get a good reading is with a really good tach. When you are full throttle the tach should come up and then back off about 5 to 10 rpms. in about 2 to 5 seconds. If it is backing off more rapidly then you have a lean condition. If it drops more than about 50 rpms. in a couple of seconds. GET OUT OF THE Throttle. You have a severe lean condition. If you see the rpms climb really slowly and never really level off then you have a rich condition. Granted. You need a long long  straight away for this type and you need a good tach. Digital. Tiny tach is ok but it only updates every two sec. I think. But they are only about 50 bucks. I have used that. The much better one is about 300 bucks. It updates twice a second I think. Do any of the sleds have digital tachs?Hope this helps. Mikuni sells a manual on jetting carbs. and you can get a lot of info on line. too.
 
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