Plug Chops

5 replies to this topic
  • sandrappy

Posted July 14, 2008 - 02:58 PM


I have a question for those of you that have done any plug chops on the yz450 motors. It seems as if i can not get a very accurate reading from doing a typical plug chop. The plug is always white until it is pig rich then it will turn a brown color. I know the bike is rich as it is a couple bike lengths slower with the bigger jets.

Anyone else do many plug chops on these bikes with much success? I can't figure out why the plug color isn't changing. Also i am running premium fuel and the same as stock spark plugs (can't remember the numbers)

  • grayracer513

Posted July 14, 2008 - 03:04 PM


You cannot accurately read spark plugs when using unleaded fuel, plain as that. The only part of the plug that will show a hint of accurate color is all the way at the base of the insulator where it meets the shell of the plug.

  • sandrappy

Posted July 14, 2008 - 07:27 PM


From my experience it has always been the opposite. Leaded race fuel is much more difficult to read as it tends to burn cleaner and leave a light tan/greyish residue making the plug appear lean. A great example is you can tell wheter a bike is running race fuel or pump gas by the exhaust. The exhaust pipes of all our bikes that run race fuel always have a light colored greyish residue in the exhaust versus pump gas bikes that are always black.

The weird thing about this yz motor (as i am new to the 450's) is that with a magnifying glass i can not even see the smoke ring (the part of the plug down by the base of the insulator you described).

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  • grayracer513

Posted July 14, 2008 - 08:22 PM


Assuming the jetting is not varied when switching fuels, the tail pipe color differences are easily understandable. Many race fuels require richer jetting than pump fuels, and this can account for the lighter color.

It doesn't take much to cause this. My '06 has a gray residue in the tail pipe at sea level/80 degrees with a 165, and black with a 168.

Here's what Addie Sisneros has to say about it:

  • bigred455

Posted July 14, 2008 - 09:07 PM


As already stated do not jet by sparkplug color,it will get you chasing your tail. I can purposely richen up my main 5 steps,and I will still show you a white plug.If you sat there running in the lower RPMS,you may get color run it hard and the color is gone,but reading the tip of the insulator on 2 and 4 strokes is a bad myth.If your insulator is white it is telling you that you have the correct heat range plug.The only time you are lean with a white insulator tip,the white will be a grainy(spelling) somewhat shiny color. If it is white like the stock color it comes with, you are fine,especially on a plug that is not that old.Infact it takes quite sometime to get color on a new plug,even a 2 stroke.

  • bigred455

Posted July 14, 2008 - 09:10 PM


The weird thing about this yz motor (as i am new to the 450's) is that with a magnifying glass i can not even see the smoke ring (the part of the plug down by the base of the insulator you described).[/QUOTE]

It really is hard to see even with a manifying glass,cut that plug THERE WILL BE A RING DOWN THERE.:thumbsup:

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