Plugs different colors?

[MFJustin]

Had a question for you knowledgable carb people. I've read and Reread the carb guide and think my carb tuning attempts are coming out ok. I've got an '81 running a set of BS38's, straight pipes and UNI foam filters. Main jet has been bumped up to a 142.5 from the stock 135. Bike idles good, as far as WOT throttle goes it pulls but I definitely feel some break up which would indicate running too rich. Mix screw is sitting at the recommended 2 1/4 turns out.

After running these plugs for awhile to see how everything would shake out, I pulled them to take a look. The left cylinder plug looks to be black but not super black, the right cylinder plug looks light-grey/whitish. I thought I remember reading that the right cylinder burns hotter so that could be the cause for a different color plug. These plugs are BPE7e's by the way. Just wanted to see if one of you more knowledgeable individuals could look at my plugs and tell me what you think. I want to drop the main jet down to a 140.0 to see if I can eliminate some of that breakup but my concern is that the right plug is coming out that color because its running lean and don't want to lean it more by dropping the mains. Bike doesn't have any popping at idle or deceleration, feels like it runs good overall but I'd rather be able to say the bike runs great instead of settling for good.

Hopefully these pics will do. Hard to get my iphone to focus on what I want it to.

 

[Grinder]

Did you check the compression on both cylinders?

 

[DaveO]

Are your plugs really ancient? There ought to be two wide faces parallel to each other like this.

AFAIK when the plug sparks it carries metal from one electrode to the other,
eventually ending up with a spike on one and a build up on the other. Presumably
the build up on yours has been filed off. If I was doing plug readings I would start off
with two new plugs. Without them you won't get a nice fat spark to burn the fuel efficiently.
I'm going to guess that a poor spark might result in poorly burned fuel and
sooty deposits (I may be wrong). You may have a carburation problem but
I would change the plugs first and then see where you are.

 

[MFJustin]

Did you check the compression on both cylinders?

When I first picked up this motor I checked it and it was right where it needed to be, can't remember exact numbers. I've barely put any time on it since then so those numbers haven't changed.

The plugs aren't coated with oil or anything, one just happens to be darker than the other and the bike runs fine in my opinion. Pardon my ignorance but wouldn't a problem with compression cause a lot more noticeable of a problem than just plug colors? I was just trying to better fine time the carbs and a slight difference in color between the plugs threw me off.

 

[MFJustin]

Are your plugs really ancient? There ought to be two wide faces parallel to each other like this.

AFAIK when the plug sparks it carries metal from one electrode to the other, eventually ending up with a spike on one and a build up on the other. Presumably the build up here has been filed off. If I was doing plug readings I would start off with two new plugs. (I may be wrong).

The spark plugs pictured came with my Pamco kit and the electrode is more of a point than a flat looking electrode like the one in your picture. I have plugs like that and can definitely swap them out and ride it for awhile and check plug color then.

 

[5twins]

You have platinum plugs. They're supposed to look like that with the tiny pin center electrode and the angled tip on the side strap. You're running rich, too rich to even start reading plugs for fine tuning purposes. When you fine tune using plug readings, what you "read" is the "smoke" or "mixture" ring on the center porcelain section of the plug .....

You want the smoke ring to only cover the bottom 1/4 or so of the porcelain. Yours is all black, pretty much on both plugs. Granted, the one is a bit lighter but it's still too rich. Go down a size on the mains and lean the needles a step if you haven't done so yet. The needles must be leaned when using larger mains on most of the BS38 carb sets. They control the midrange and will have a big effect on the size of that smoke ring. Get it jetted and tuned closer and your plugs should start resembling this .....

The top portion of the porcelain will remain white at 1st and eventually color light gray or tan over time. The ring at the top of the threads will always be black, that's normal and isn't even looked at when plug reading. The side electrode will keep itself burned clean and eventually take on a light gray or tan color. Although you can't see it in the pic, these plugs have a nice smoke ring near the bottom of the porcelain.

 

[MFJustin]

5twins thanks for the info, I did some more reading in the meantime and learned more about the smoke rings. I'm going to play with my carb settings some mor to see if I can get rid of the stumble and then I'll make sure to pay attention to the smoke rings.

 

[Grinder]

I used the iriduim plugs that came with the Pamco kit also and they always looked black as yours. I switched to Autolite 63's without doing anything else and the color improved alot. I think the 63's are a little hotter plug and a whole lot cheaper.

 

[ontherocks]

You need to cut off the threads to see the ring. Do some dead cylinder adjustments to get bike running properly. Here is the link to when I was going through it and got some great advice from the gurus here. My bike runs perfectly now

http://www.xs650.com/forum/showthread.php?t=13510&highlight=ontherocks

 

[MFJustin]

I actually read through your entire thread already after a little searching around. Definitely some solid advice in there, I'll be honest I wasn't aware that plugs should be read based on the smoke ring. Always learning something new on this forum. I'm going to drop my main down to a 140 and lean the needle out one slot and work from there.

My bike felt as though it was running pretty solid although I knew I was running rich because of the stumble at WOT, now it's just the process of fine tuning it but I feel a whole lot more confident after reading some of this info!

 

[5twins]

You don't mention the year of your carb set but by the jetting sizes and mix screw settings mentioned, I'm assuming they're a '78-'79 set. If so then you absolutely need to lean the needles a step if you increase the main jet size at all. Leaning the needles may then call for one step up on the pilots. The overlap of adjacent carb circuits is what's at play here .....

The mains influence the upper midrange as well. Increasing them makes that area too rich and results in stumbles. Leaning the needle setting fixes that but at the same time it leans the idle to midrange transition area. That can result in a flat spot just off idle which will require a size up on the pilots to correct.

 

[MFJustin]

You're correct they're the 78-79 38's. I'm going to drop the main down to 140 and lean the needle out by one slot, right now it's in the third (middle) slot, I'll keep a look out for that flat spot off of idle.

 

[5twins]

Grinder and several others have mentioned those iridiums burn dark. Maybe the heat range isn't quite right for our 650s? They're supposed to be good plugs but at around $8 each, they'd better be. I never went for those fancy expensive plugs. I just use the plain old regular NGKs. They're readily available at most auto parts stores today and usually a little under $2 each. I don't buy them from cycle shops, they charge near double that.

I've found this bike to be tough on plugs, wearing them rather quickly. Maybe it's due to it being such an old design. While I still had points, my plugs would be showing signs of wear in as little as 2000 miles. Now with a Pamco and better coil, I can go about twice that but I usually change them out by about 4000 miles.

Determining whether your plugs are worn can be difficult. Once the bike is in a proper state of tune, they burn so clean and wear so uniformly, it's hard to see the wear. That's why I always keep extra new plugs on hand. Besides the obvious reason of having a new plug to replace one that fouls or craps out, I use them for comparing to the current ones to discern any wear. As they wear, what happens is the center electrode gets shorter. This is difficult to see when looking at a used plug by itself but easy to notice when holding it side by side to a brand new one.

NGKs are sold in 4 packs and that's how I buy them. Two to use and two for spares. When the spares get swapped in, I go buy another 4 pack.

 

[DaveO]

Thanks for the information on the Iridium plugs, 5twins.

 

[Jack]

You need to cut off the threads to see the ring. Do some dead cylinder adjustments to get bike running properly. Here is the link to when I was going through it and got some great advice from the gurus here. My bike runs perfectly now

http://www.xs650.com/forum/showthread.php?t=13510&highlight=ontherocks

You do not have to remove the threads to read the plug