I have a 103" 2010 Limited.
When should I consider changing plugs and with what kind and number?

 

Standard Harley Davidson spark plugs gapped at .040 every ten or twenty thousand miles. I got over 30K out of my original plugs and replaced them just because. In the old days, engines with breaker point ignitions required fresh spark plugs to run right. Modern electronic ignition systems are easy on spark plugs so they're not much of an issue in stock engines.

 

Check and gap them with every service. You will know when to change them, and probably do it long before you have to.
The stock Harley plugs are fine, not a whole lot of money to save going aftermarket.

 

The HD std. plug is a 6R12 if i'm correct.

 

The stock 6r12 supposedly has ion knock sensing capability that aftermarket and gold/platinum H-D plugs don't. If the dealership is convenient I'd stay with stock plugs for the few $ cost diff. Like others said, stock plugs last a long time but I did change mine at 6k miles when I went to 103" /cam/head/tune..

 

Should run fine with stock number plug. In fact if you look in manual Harley probably says no substitutions. They do not mean just a Harley plug , what they mean is correct number. If you go to another manufacturer always make sure it's plated.

 

I put e3's in mine and they seem to smooth out the idle

 

The plugs themselves don't have ion sensing capability, but the electrical characteristics of the OEM plug are factored into the function of the "ping" sensing circuit, so changing plugs could have an effect on the system. I've used HD 6R12's, 6R10's and the Autolites, I have noticed no obvious diference in performance among the three. I can't validate my claim with dyno sheets for comparison, so take it for what it's worth. Only thing I can tell you for sure is the OEM plug works fine, and the ignition sytem is one of the things the Factory got right with the late model EFI Twin Cams; the ignition system is very robust and not much room for improvement. As far as life expectancy or interval for replacement, what ever you decide, you will probably change them long before the end of their useful life.

 

If you think you need to, for peace of mind, change them. Don't cost too much and plugs are one item should probablly use stock. Don't forget anti-seize and torque 'em. Good time to upgrade wires to Screamin' Eagle type. May need the zip ties for the wires also.

 

Good Info