Plug Color - Too lean or ok?

[Sci85]

Hey guys, so I've been working on the jetting of my recently finished 550 to 673 conversion and it's currently running fine. No issues whatsoever. And no pinging on 93 pump gas either. However, I pulled the plugs today (less than 20 miles on them) to take a look and I'm wondering if I'm too lean based on the color below (outside plug & inside plug).

When is lean too lean? If there's no pinging or problems otherwise, should I leave it or try to richen it up just a bit?

[hjfisk]

I personally would fatten those up a little. Some would run them that way .

[tkent02]

Were you going at wide open throttle, or cruising, or putting around slow right before you pulled the plugs?

Or did you do a proper plug chop? If so which throttle position?

Plug pictures are difficult, for instance the lighting in your two pictures is different.

[Sci85]

Those are two different plugs as mentioned. An outside and an inside. This is mixed driving. Some WOT, some idling but mostly light throttle. I was wanting to get an overall general feel not a single throttle chop. I will say that it runs good at all throttle positions currently. I think they look at little on the lean side but wondering if it's worth the effort to pull the carbs again if they are close enough. Will running lean hurt anything if there's no pinging?

[tkent02]

Running lean can burn things up. I have an 850 piston with a half inch hole in the top from running lean. He got an air leak in Patagonia, it was the end of that engine…
The plugs change color quickly, within a few seconds at a different throttle opening they will have changed. So if you ride around an hour and then let it idle a minute before you pulled the plug, it will show only the mixture at idle.

Do a proper set of plug chops, and you will know.

[Sci85]

That was actually coming in on light throttle cruising. I killed it and coasted in because I didn't want any idling color.

I think I will go ahead and pull them one more time and richen up the needle just a bit.

[tkent02]

That was actually coming in on light throttle cruising. I killed it and coasted in because I didn't want any idling color.

I think I will go ahead and pull them one more time and richen up the needle just a bit.

If that is at light throttle it's rich enough. Go test it at wide open, that is the important one for avoiding engine damage.

The 650 got away with being pretty lean at low throttle, mine were always white and it never had a problem. Really lean at very light throttle hurts nothing. There's just not very much heat in there.

Making a lot of power is where you need a bit of color, and where you can't afford to be too lean.

What main jets are you running, and what was stock for the 650? Stock was 110 on the '81.

What intake and exhaust?

[Sci85]

That makes sense. Thanks tkent.

I have dynojet mains installed. 155's. I do have 160's in the toolbox. 110 was stock for the 650 but that's a Mikuni jet. Intake's are K&N twins and mac 4 into 1 with a straight through baffle. If the weather gets good, I will go find some place where I can take some WOT chops. It runs good and WOT and again, no pinging but that makes a lot of sense about wanting to be a little on the rich side at WOT.

Quick question, do you know how long you need to run at WOT to get a good color indication?

[chuck hahn]

Bottom one is what you want to see..just a hint of brownish tan at the porcelan tips. One is way too rich.

[tkent02]

There is a whole lot of info to be gleaned from plugs, different areas on the plugs, the electrodes, base of the porcelin, etc. Mixtures, timing, a lot of stuff. It's a bit like rocket science, and I am not an expert. Have played with it some, and read about it some, tuned quite a few bikes. I would suggest spending a few hours reading about it.

The low power stuff is more about fuel efficiency, throttle response, ride ability. The high power stuff is about performance and avoiding engine damage.
It takes time and effort to get it all perfect, but it's worth it.

[chef1366]

There is nothing lean about those plugs.
Twenty miles? Good color.