Spark Plugs
 

Changed old plugs (screaming eagle ) with new plugs (screaming eagle) , bike runs like crap. Stumbling and throttle response is worst. Put old plugs back in and runs great. Repeat and same crappy results. Bought new plugs and same thing. Any ideas? Possible tune (fp3) is for old plugs lol? Gap for plugs looks to be same. Im baffled :icon_werd:

By some 6R12 plugs from HD and try that. Gap them around 35 to 37 thous.

Use a plug gapper? Don't trust them to be gapped out of the box.

Try changing one plug at a time to id the faulty plug.

Sounds like you didn't set the gap.

It's something you did..Probably way before the plugs..like your tuner engineering

You could try buying something other than that grossly overpriced MoCo crap. That generally is the best way to get quality parts that just work as advertised.

Put two stock HD plugs in it.

Who would ever trust the gap out of the box, I am not saying the OP did, but you stated looks to be the same, gap them with a feely gauge.

If you hadn't tried a second pair of new plugs i'd thought it could have been cracked insulator or other plug issue.

First double check the gap.

You could ohm out the plugs, tip to tip. compare to the old ones, maybe the parts store got a bad batch. Where did you get the plugs from? If you got them from the internet, they could be knockoffs made on the Ho Chi Mihn trail .

I'm guessing a cracked insulator or manufacturing defect in some way in one of them.
One time I got one that the center electrode would move up and down, hitting the ground electrode.

:icon_that: Gettin' ready to do my 20K (at almost 21K) service, just bought all the oils, filter and 2 new HD plugs, first time I'll be changing them. Bike runs fine, I don't expect much of a difference. I looked in the manual, IIRC gap was between .037-.043, I'll aim for the middle. Also bought 2 new Dunlop OEM tires, Indy gonna change those for me. 15% Military discount plus $115 Dunlop gift card lessened the pain. Good luck to the OP, curious to see what the outcome of this is...

Have gotten bad plugs before, ran like chit, but two is odd, like stated, bad batch ?? Possibly

Checked old plugs , they were gapped at .042 New plugs were at .038 . Re gapped new plugs to .042 .Didn't think .004 would make a difference but did. Do you guys think i should rerun auto tune or no? (FP3) Thanks for help btw.

Sure, try only things that automatically do for you..

Wow, I thought that would be close enough. Glad they made a diff.

Ion sensing?

So are you saying the gap change from .038 to .042 fixed the problem, no more stumbling? They give you a range and you were well within the range with both plugs, it shouldn't have made a difference at all. Did you do or change anything else?

Sure you had the wire clicked on the plug? Just asking, .004 difference would not make a bike run like you have described.

I would bet it was this...... ^

Also, if you have a '14+ touring bike, they are known to have the gas tank rub through the front plug wire.... when you changed plugs, you could have change the wire to short out, and when you gapped the plugs, changed the wire so it's not shorting out.... I'd check the front plug wire..

My (new to me) '16 Ultra Classic at 16K miles....

https://farm1.staticflickr.com/851/4...857a8dfd_c.jpg

I always place a piece of fuel line over the plug wire to prevent this from happening.

The wire rubbing the frame isn't just a 14+ thing. It's literally been a thing since like 07 (or even before), and HD did nothing about it in all that time until just recently. I guess.

Good to know....

Only other touring bike I've had was a '12 Limited. I had that tank off several times, and never had a worn spark plug wire... I must have been lucky..!

Thinking back now, maybe it was in 08 with the introduction of the 6 gallon tank. I forget.
Regardless, not everyone had the issue but it was reported enough that HD should have done something about it. Both my 09's, 10, and 14, and now 17 wires rubbed. Guess I'm the lucky one. ;)

If I read the OP correctly he stated he went from standard Harley plugs to the SE plugs. The SE plugs electrode is maybe 20% as wide as the standard electrode, so that .004" difference is greatly amplified, I would almost recommend opening it up another .003-.005". As well as they can cause the ION (knock) sensing to be problematic.