I just added these pics to another post about missing and popping, but thought I'd add a new post devoted just to the odd look of these plugs. Opinions on what you see?



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Well the one that is dark is running a tad rich and the one that is white and appearing to be a bit brick red is a good fuel mixture. I would say it is fine just not trimmed.
When did you pull these I.E. after idle time, killed on WOT, killed on a steady cruise mid throttle. Im guessing pulled after a idle. I have not read your other post nor know where you posted it, maybe you gave more info on it.

 

To me, the white one is lean and the brownish is running closer to normal. The whiter one also looks to have a little problem with possibly fuel deposits.
Anyway, I'm no mechanic and here is a link that may help.

http://www.centuryperformance.com/spark2.asp

 

Even though the pics are good, still hard to tell not actually seeing them. That being said, the first one with a little soot is border line rich, but acceptable, hopefully it came of front cylinder, second one shows high speed glazing, plug is too hot, or mixture too lean and if from same bike at same time, very likely have an intake leak on that cylinders intake.
Note: should always put anti seize on your plug threads!

 

Thanks all, for your feedback. Mopar and Reese: Here are the missing details.

Plugs were removed following several minutes of agressive riding and a few minutes of ldling.

98 carb'd 1340 motor with mild cam (.5" lift, 240 dur) V & H Short Shot and SE filter.

Steady-state mid-RPM cruising I get an occasional miss (once ever 5 seconds or so, but not like "clockwork") and occasional popping through the exhaust.

There's no x-over between pipes and the inside of the rear cylinger exhaust pipe is noticably (but not dramatically) blacker than the front.

On cold idle, rear cylinder doesn't seem to fire fully as evidenced by the sound of a hard "hit" on the rear cylinder every fifth revolution or so (place your hand an inch from the exhaust and you can feel it hit harder).

Compression is great and within 3 lbs per cylinder.

Wires are Accel. Rear wire (shortest one) has 60-ish ohms resistance, front has 250-ish ohms.

The timing "seems" about right, but it's so damned hard to really see those marks. It does seem to wander a bit, but I associate that (perhaps wrongly?) with loping at ide.

Rear cyl spark pug looks like it's leaner than the front but I hear that's normal (rear cyls run hotter, no?). Front plug has a region of dark black on one edge of the insulator, rear cyl has a region of dark tan. I assume this is just indexing and is normal for these motors?

So... what do you think?

 

Few minute idle time your reading mostly your idle. Your complaint seems to be mostly cold start running and steady cruise. If you do a run at temp and kill engine while running at a steady cruise no decel or idle time you will get a better read. ( recomend a good stretch of road with a known parking lot you can pull into.)

Im not a Harley mechanic nor have I checked specs on a 1998 model. But to have unequal resitant wires as a spec would seem very odd. This is where I would do research in finding what the actual spec is. I have no idea what the specs are but I would assume they would be even and I know there is a range in resistance desired. Not saying this is your issue but I would look into it thoroughly,. Was noted above you may have a vacuum leak. Vacuum leaks can cause issues like you seem to be dealing with. There are various methods for finding a vacuum leak. I generaly use a carb cleaner and spray small amounts around vacuum hoses,connections,seals etc anywhere a vacuum leak may occur and listen for a rise in rpm. Hear a rise in RPM and you found a leak.

Im not familiar with a 98 harley ignition system but I think I read somewhere it used a crank sensor or cam sensor and was controled by a module. So Im not sure but believe it is not easily adjustable (needing a aftermarket control unit or a flash of some kind).
Seeing as your rear plug (60 ohm wire) looks like a average 14/1 burn ratio and your front plug (250 ohm wire) appears to have a rich or non complete burn look, I would seriously look into those resistance specs. A check for a vacuum leak is also a very good idea.


Hope you figure out your issue and get the worry out for mind at ease long rides, take care.