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Secondary Plugs


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I just finished up my 6000 mile service. Exhaust valves were predictably a little tight, one loose intake valve was adjusted and I made a very minor high rpm sync adjustment.


The plugs were a surprise for me and I'd like to get a little feedback, if I could, on why the primary plugs look good with a light tan color, while the secondary plugs look fuel splashed.


I don't know much (anything) about how the twin spark system works, so as far as I know the appearance of the secondary plugs may be completely normal.


The bike is running flawlessly with good power and gas mileage.


Here is a picture of the plugs; secondary on the bottom.



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My '04 looked like that also at 5000 miles. I think it even had a hotter plug in the bottom. After changing the plugs at 5k, they looked normal from then on. Theory was the bottom's got somewhat fouled during break-in. I knew there was something wrong at 5000 miles as my '04 started surging. New plugs on the bottom were the cure. thumbsup.gif

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I would say that you have an issue. I have done all the service on my RT (now just shy of 19k) and the secondary plugs have never looked like what you show. In my case the secondary plug have been only slightly less perfect than the primary plugs. Looks like yours have not been firing.

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I wouldn't worry. You are probably still seating the rings and any oil seepage past them between startups is gonna cuddle up to the secondary plugs. Mine looked like yours at the 6k service. I just swapped the primary & secondary plugs so the slightly fouled plugs could burn clean. I'm thinking that after the 12k we probably won't see as much difference between the primary & secondary.





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Seems unlikely that the secondary plug is supposed to look that way. I don't agree about the rings seating. Your rings are 80% set at 100 miles and by 6000 it's too late for them to seat. If they're leaking now you're looking at a ring job. But I don't think that's it. Has your dealer checked for error codes? What about the other cylinder? Are they both running this way? I have not picked up my R12 yet (next week) so I have not looked at the ignition closely. Are the secondary plugs on the same coil? Talk to your shop and see what they feel the explanation is. Good luck.

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The secondary plug lives in a part of the combustion chamber where swirl is not really doing a good job of keeping the mixture homogeneous. Kind of a 'dead zone'. In fact, that is why the plug is there as it helps remove unburnt fuel. It is normal to see this little bit of soot. My '04 did it all of the 65K miles I had on it.

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So I take it this is from an R1200RT given that you're on the hexhead forum. Correct? The secondary plugs on my RT have never come close to looking like yours let alone have unburnt fuel on them. This is not advise, only what I would do if I saw this on my bike. I would investigate whay these plugs are not firing. The plug in the bottom photo was not firing. Compare it to the spark plug photos in any automotive manual and that's what it will tell you. You say your bike is getting good mileage. What's good mileage? What is it getting? Under what conditions? Oilheads have run with single plugs for many years and there's no reason why they will not run on one plug per cylinder now. However, with the new engine management system they run a lot better(and cleaner)on two per cylinder. BTW, my RT has never gotten any worse than than 44.11 mpg and has gotten as high as 56.18 mpg. Yes, I do track the gas mileage on my RT everytime I fuel up.

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I haven't had the shop run codes for me yet. They are backed up and my appointment is a few weeks away. The secondary plug from the other cylinder looks exactly like the one in the photo.

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What were you doing before you pulled the plugs? Did you go for a ride to warm the oil to change it (possibly just tooling around the neighborhood)? Did the bike sit for 15 minutes idling? There's can be other explanations for the look of those plugs that aren't neccessarily indicative of a problem.

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The bike is 3 months old and I started the 6000 service the morning after I returned from a 730 mile day trip to OKC and back. I do not baby this bike and I don't sit in traffic much these days since I've been out of work.


I'm swapping out the plugs today with new ones and will alert the Lone Star team when I take it in to run codes and check for software updates.


I'm really not too worried, but I will pull the secondary plugs again in about 2000 miles for a quick inspection.

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