I have a Harley Davidson Xr1200x Sportster which I just got. Changed the oil also tranny & filter as I couldn't find last date of service coang of oil. So yesterday I checked the spark plugs they were clean. But the mechanic cleaned them & said the needed gap them as one was too narrow. Mind you I had no issues at all. Gapped them at 0.40 now I'm not getting the same smooth sound or feel as if it's miss firing. I have iridium spark plugs okn my bike should I change them to NGK or get another set of iridium spark plugs.please advise..