Spark Plug Reading Gurus

When I first got the jeep, it was getting 5 mpg, sooty black plugs. So I've been tweaking a little here, a little there, fixed vac leaks, header leaks, non existent choke replaced with one that works properly, time, tune with a vacuum gauge, etc, etc.
The pics are where I'm at now. I'm pretty happy, HUGE improvement. All three photos are of the same plug, all 5 other plugs look similar. My question is this. Why is one half of the plug white, indicating lean, and the other half brown, indicating slightly rich, maybe. I thought this could have something to do with running headers, until I happened to pull the plug in my chainsaw yesterday, and the plug looked just like the ones from the jeep. California formulations of fuel are changing constantly, would that have an effect?

It's been a few years since I've read plugs, thanks to fuel injection, but I don't remember plugs looking like this in the old days. Then again, there's a lot I no longer remember about the old days. Any words of wisdom?

 

the spark plug hole is not centered directly in the center of the combustion chamber; consequently, the side of the electrode that gets the "blast" is the side of the spark plug that shows combustion/carbon/deposit buildup.
BTW, the plug looks perfect, good job!

 

Makes perfect sense. So much for my memory! Thanks for the confirmation on my read, Jim. This was one of those deals where it wasn't one thing that made it better, it was a whole bunch of little things that all added up.

 

I am no expert, but that gap looks huge!
Maybe I am just used to newer engines?

 

Yep, big gap. DUI.

 

I think a touch lean. The tan is also fuel additives and oil deposits. How many miles on those plugs. What type of driving were you doing just before pulling plugs. Overall they look good, just a little lean in my opinion.

 

A little lean would be a good thing. I decided to really get into this rich/lean issue after participating in the "Density Altitude" thread. I live at 3500 and use the jeep from about 1500 to 8000 ft pretty regularly. Mountain roads (55 mph max) and trails. Temps here run from the low teens to 115* in the summer. A lot of variation for the old carter to deal with.
On the day the plug pics were taken, the wife and I went out for a little trail ride about 70*, we got up to about 6000 ft. Drove home at a normal rate of speed, cut off the ignition and coasted about the last block home, pulled the plugs. Since I'm not a racer here, I figured I should just check the plugs after driving in a normal manner, instead of after WOT.

I've heard the old YF's are pretty decent carbs, so I really wanted to try my best with the stock setup before making a new metering rod or switching to a hotter plug or advancing the timing. I figure if you're correct, and I'm a little lean at 70*, hopefully I won't be running too rich when the outside temps reach 90-100*, which is most of the spring/summer/late fall, when the jeep gets used the most. I'm just going to have to wait for it to warm up and check again.
Thanks for the input!

 

It's hard to tell for sure from your pictures. But if you look at the base of the ground strap it appears to be a little rich. That being said, you are very very close to being as good as one can get.







good luck

 

I like to look at the ring down inside the plug. My understanding is the shorter the ring the leaner the motor. Here is a pic from my snowmobile plug. I took the pics to allow some web tuning. The bottom burn marks on the porcelain are where I cut the plug with the die grinder. The ring I am referring to is the one at the bottom of the porcelain exposed in the chamber.

 

http://www.theultralightplace.com/sparkplugs.htm
http://www.4secondsflat.com/Spark_plug_reading.html
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
http://members.uia.net/pkelley2/sparkplugreading.html
http://www.ingfatrygg.se/Spark_plug_diagnostics.html

 

Great links. thanks fuzz!

I had no idea how much you could learn from plugs. A couple of those links provide info way, way beyond the simple picture charts you see everywhere. An art, I guess, kinda like tuning with a vacuum gauge.

From reading my plugs in real life, vs. a photo, I think I can advance my timing a couple of degrees to get things closer to perfect. When it gets warmer, I may have to move to a hotter plug, maybe 1/2 step hotter. I'll wait and see.

What I'm learning here is that you can pretty much nail an outstanding tune with a vacuum gauge, a simple timing light, and the Mark 1 eyeball plug read.

 

Post up your new mpg calculations whenever you get them figured. Looks great, way to go!