I was having cold starting problems,and a clunking sound on the rear cyl when starting and still get that clunk until it warmed up,then no more noise and ran good. I put in new NGK plugs,gaped.035,antiseize,also replaced cap and wire to the back cyl,I saw it arcing out. Now it starts right up and stays at idle without me having to give it gas and hold trotle.I still get a few ticks not clunks for a few seconds on the back cyl.? But otherwise it starts right up now,hot or cold so I will just keep riding it.I also get less popping on decel .I dont know what that noise is,only cold starts.So thanks to you guys,these plugs seem to have made a difference already. Paulywog.