I have just fitted these to my Harley and am very impressed! Starts immediately, pulls soft and hard! I used them on my 103 before and they weren't any different from the 6R12, but now I have an S&S 124". Now it's very different. My new engine responded really well to these plugs. Oh, and as for the gaps The packaging doesn't even say DO NOT HEAL THESE PLUG I have used SE plugs and 6R12PP plugs and these NGK plugs are the best in my opinion.
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