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This article was revised on 06/04/2014 and 05/21/2017, by the author

Numerous problems can occur if your engine's spark plugs are not correct or not working properly.  Spark plugs are 'read' by looking at the combustion chamber end of the plug. You can look at the color and deposits from combustion and determine a fair amount...with some practice.  It is not just the condition of the normally near white or light tan or orange color of the central electrode insulator, but the condition of the outer and central electrode and the color and look to the metal on the flat end portion of the spark plug, which is about 1/8th inch wide. Once you gain experience [it doesn't hurt to ask SEVERAL supposedly experienced mechanics to confirm your analysis], you will find that much can be learned from a look-see. Spark plugs are looked at to determine if they are worn to needing replacement; to see if the engine seems to be operating correctly; and to get some idea of specific problems.  Reading spark plugs is somewhat of an art, requiring experience, especially with modern unleaded fuels, most of which contains alcohol and other ingredients that makes reading spark plugs more difficult, as the 'old colors' do not always apply.  SOME things never change, however, so, read on. 
You should have a working knowledge of spark plug heat ranges, proper torque setttings, whether or not to use an antiseize compound on the spark plug threads; and what the proper spark plug caps are for YOUR motorcycle. 

 
NOTE: An in-depth article on spark plugs, problems with newer Bosch Spark Plugs; and chart of all three Bosch spark plug numbering systems; chart of Bosch versus NGK; and a listing of NGK spark plug caps,  and much more, such as use of antiseize compound, etc., is here:

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