i put 10mm wires and screamin eagle plugs and got better fuel mileage

 

I thought I'd blow the dust off of this thread and chime in with my experience using Iridium (fine wire) plugs.

I've always used standard NGK or Autolite plugs 1 range colder since I'm at 10.5:1. About 1200-1500 miles ago I tried a set of NGK Iridium plugs just to see for myself how they'll perform. At first they were great, it seemed the bike started quicker and it had slightly better throttle response. A couple weeks ago it started running a bit rough at idle and I started to hear a thumping or knocking sound which was worrisome since I was thinking Compensator or worse??? I last rode it over the weekend and the thumping/knock was a little louder and it was running a little rougher at idle. At the end of my ride I had an engine light come on. After giving it some thought and knowing the mixed reports on the Iridium plugs, I replaced them with a new set of trusty Autolite 4163's. After I installed the new plugs (gapped at 36) I crossed my fingers and hoped the plug change would solve the problem. Even though I did not have time to ride the bike today, when I started it up, I got my normal idle back, the thump/knock was gone and the engine light went off in about 5 seconds. I won't be going back to Iridiums again.

 

Kind of smells like the HD debate of fossil oil vs synthetic, from 10 years ago.

 

I switched back to stock plugs. My NGK rear plug broke. the insulator separated from the rest of the plug and turned the gap to zero when right side up.