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I've tried many of the specialty plugs on the market. Never found any to be seat-of-the-pants performance gains. In my opinion stock plugs properly gaped are just as good as any. They are cheap and I change mine often. Having said that, I once upgraded to a SE coil on my 03 Night Train. The higher output coil allowed me to increase the plug gap producing a larger spark. There was definitely a difference in performance.
Slideshow: Jason Momoa's latest restoration project blends 1920s Harley-Davidsons with modern electric technology, creating some of the most unusual hybrid motorcycles ever built.
Harley-Davidson Fat Boy Becomes a Dark, Decepticon-Inspired Custom
Slideshow: Killer Custom's latest build relies on styling changes rather than performance upgrades, giving the cruiser an entirely different personality.
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Slideshow: The bar-and-shield logo shows up on far more than motorcycles, some of the company's most unexpected products have nothing to do with riding.
Slideshow: From the troubled AMF years to modern misfires, these bikes earned reputations for reliability issues, questionable engineering, or disappointing performance.
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Slideshow: The Swiss custom shop has taken a Harley Softail and stretched it into something so long and low that it looks closer to a rolling sculpture than a conventional motorcycle.
