Re: Spark plugs

Posted by hendred on Jun 24, 2020; 5:15pm
URL: http://silk-motorcycles.221.s1.nabble.com/Spark-plugs-tp5001960p5001961.html

The answer to your last question is probably not.  Owners will have their favourites just like which oil to use.  The plugs listed in the handbook are all obsolete now.  I can't find an old NGK catalogue to find out what the C in B8HC stands for.  It could be copper cored.  Looking at plug cross references B8HS is the modern replacement for B8HC.  The S stands for a standard copper core electrode.
The problem as I see it is how modern plugs stand up to fouling.  NGK plugs have a reputation for not being very good if heavily fouled.  If the engine is set up so that it isn't over oiling and the air fuel mixture is ok then they seem to work ok.  Which is your experience I believe.  NGK  B7HS or B8HS work ok in my Silk as long as I put a new set in at the beginning of the riding year.  If left in the engine over winter  they start ok but fail after the first run.  I believe it is something to do with combustion salts on the insulator and/or oil.  
I am currently trying NGK BP8HS plugs, not because of problems with B8HS, but because there is a theoretical advantage by moving the spark further into the combustion chamber.  It has reduced the four stroking at small throttle openings but not cured it.  Probably need a bit more cutaway on the slide.  
Fine wire electrode plugs spark at a lower voltage which can be an advantage and some can withstand more fouling.  I am using Champion L3G , which is readily available in the UK and has the same heat rating as B8HS plugs, in my MZ.  The reason for doing so is that under certain conditions the ignition system voltage drops and the lower spark voltage of the fine wire electrode overcomes the problem.  The engine runs very well on the plug which is added bonus.
In conclusion, if the NGK B8HS works well for you why change?  They are readily available and cheap enough to have two spare sets stored in the side panel pockets.