E3.34 spark plugs

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Oct 28, 2014
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I have a 1966 atlas which runs very well. My standard plug is the NGK BP7ES, used them for years. I am usually skeptical of fancy spark plugs but a friend gave me a pair of used Denso iridiums and the bike ran better and started better. The color was good. Another friend gave me a pair of E3.34 plugs and they ran even better. Most driving in town. However, they appear bright white which would tell me it is a heat range too hot. The package says they replace BPR5ES, 6ES, 7ES, definitely running to the hot side. Also, I don't see how a plug could cover those ranges. I would never dream of installing a 5ES and have only rarely used a 6. The Champion crossover is RN9YC, 11YC, 12YC.

I have removed the plugs even though they are the best plugs I have ever used (short duration) . So what's going on? One possible idea is that modern gas is much different than what was available in 1966 and performs better with a hotter plug.
 
Better to be safe than sorry. Those plugs are too hot. I am running a set of Irridium fine wire electrode plugs and they seem to do exactly what they say.
 
I put the DENSOs IW22 back in and it runs great. But the E# plugs out performed them. Waiting on a new belt for the belt drive
 
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