The plug shown over on the triumph rat forum is an R44XL. It is the equivalent to a Champion RN5C. The resistor version of the N5C. This is two grades hotter than the recommended N3C. This alone could make the motorcycle ping (suffer a good case of detonation with either seizure of move on to pre-ignition and a holed piston) if the bike was lugged!!!!! The incorrect grade of plug is a leading cause of pre-ignition.
It would not be wise to make any diagnosis, or changes until the correct grade spark plug is offered. When you build a house you start with the foundation. In this case it is being sure that you have compression, the factory recommended jetting, valves adjusted and timing set.
Before anyone making comments or suggestions one must go over and look at the pictures! The ceramic core is chalk white. The ground electrode is chalk white from heat. There is a little bit of the grey carbon residue one would typically find on the edge of the steel body. You do not have to log onto the forum just click the link below:
http://www.triumphrat.net/members/albums/62616-open1mind/1969-bsa-plugs-carbon-20617.htmlMost of his pictures show little but the third one from the left - top row is telling. Notice that the ground strap is white and the heat soak into the body appears to be at least 6 threads.
http://www.aussiefrogs.com/forum/at...65d1414285464-reading-spark-plugs-p2.jpgAlso "reading" a plug requires a lot of experience with the particular engine and fuel being used. Google "spark plug mixture ring" or "jetting ring". This jetting ring is related to teh "self cleaning" temperature of approx. 500°C. The mixture ring forms at the point the ceramic insulator reaches 500°C and it is the ring of carbon on the plug that has a temperature lower than 500°C that we read.
Also "reading" a plug requires a lot of experience with the particular engine and fuel being used. Google "spark plug mixture ring" or "jetting ring"
http://www.roost.si/articles/jetting/http://www.ngkntk.co.uk/index.php/problems-with-the-firing-end/Because modern fuel has no lead, and that it is the lead that did a lot of the coloring plugs back in the day, spark plugs rarely look like the ones on those old plug pictures copied and posted to the web.
As a side note for those who hunger for that chocolate brown electrode please read Kevin Cameron's comment:
"For plug reading, it is essential that you begin with clean fresh plugs. A dark plug will not lighten to indicate a correct or lean mixture, so used plugs are useless for mixture assessment. Also, forget all the plug manufacturer's four color advice sheets about chocolate-brown. That is the color a plug assumes in a street-driven bike with hundreds or thousands of miles on it. The color you are looking for in main-jet tuning is white. If you make a top speed run of 30 seconds or so, and your fresh plugs come out brown, your engine is hopelessly rich."
Bottom line get the right heat range plug. Verify that the jetting is correct for your model. And make sure the bike is in a good state of tune. Then, and only then, make appropriate changes.
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