How to read a sparkplug

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8541Hawk
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Joined: Sat Jul 21, 2012 5:21 am
Location: Bella Vista, AR

How to read a sparkplug

Post by 8541Hawk »

With all the modern advances like fuel injection and O2 sensors there is no need to read plugs on new bikes.
Which means the proper way to read a plug is or has become a lost art. We have all seen the charts that show the different tip colors but they usually stop there.

While a good start, it is only part of the information available. I don't know if you guys have ever seen the old timers pulling out the magnifier and light to look at the plugs.
No it's not because they had poor eyesight or needed a better view of the tip. Instead they are or were looking at the insulator inside the plug body.

Once you have a tan tip (or here in the states they like to turn gray....which is also fine) install a fresh set of plugs. You can only get a proper reading with new plugs.
Do your run and pull them out. Now first you need to understand that the tip of the plug is the hottest part of the combustion chamber. As you travel up the insulator it cools.
What is going to happen is somewhere on the insulator there will be a black ring where the insulator has cooled enough to have the small amount of free carbon (which you want) stick to it instead of being burned off.

The closer the black ring is to the tip, the richer you are running. The closer it is to the bottom of the insulator, the leaner you are running.
So "perfect" is the tan or gray tip with the black ring approximately 1\4 to 1\2 way down the insulator. The reason you need new plugs is that once the black ring is there, it will not burn off. Which means you will not get a true reading the second time around.

While a bit of a pain it is the only way to really know if you are on the verge of going too lean before it causes you a issue. :thumbup:
Loud pipes don't save lives, knowing how to ride your bike will save your life.
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KermitLeFrog
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Location: Hexham

Re: How to read a sparkplug

Post by KermitLeFrog »

We always used to set up our racing two strokes this way. They were very sensitive to squish clearance, ignition timing and, obviously, jetting. Timing was always to factory specs and anything clever usually ended up with a neat hole in the middle of the piston. Having the minimum squish clearance was a big way to make up ground and it allowed you to lean out the mixture on the main jet which widened the powerband considerably. I still have my jewellers loupe but don't use it any more...
"I spent a lot of money on booze, birds and fast cars. The rest I squandered" (George Best, RIP)
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E.Marquez
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Joined: Wed May 30, 2012 1:27 pm

Re: How to read a sparkplug

Post by E.Marquez »

If your going to try this, id suggest using a constantly available no additive race gas.

The additives in modern pump fuel (at least here in the US) makes reading a plug unrealistic add in the gas formulations from brand to brand differences and let the tail chasing begin.

Brand new plug, using the plug chop method and a non additive gas,,,and plug reading really works :clap:
Nice reminder Mike
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VTRDark
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Joined: Sun Mar 18, 2012 9:24 pm

Re: How to read a sparkplug

Post by VTRDark »

Also with Irridum plugs this is not as accurate to read so the old style plugs are required otherwise this is a redundant method. Old school and works if you have old school plugs.

A nice link here on plugs:
http://ngksparkplugs.com/about-ngk/spark-plug-101
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