Spark Plug reading

[trevarthan]

Hello,

We've got a bit of variation on our plugs after the carb rebuild.

This is plug 1: https://youtu.be/JvkZGn-QC-E

And this is plug 3: https://youtu.be/gQVyJhMcA1c

Plug 1 looks pretty lean to me.

We bent the rochester monojet metering rod arm a bit to make it richer a couple of weeks ago, but I'm not seeing a difference in plug color.

Will a lean plug start showing as less lean if the mixture has been corrected? Or does it get burnt permanently and should we install new plugs and run it for a while?

Thanks!

Those don’t look that abnormal by my eyes—-at least when compared to the horror show of spark plugs I have seen. In any event, plugs are cheap and I would retest with new plugs so you have an accurate baseline.

[HO455]

Unfortunately in these modern times of ethanol gasoline, every brand having a different mix of additives, and the change in fuel mixtures for the different seasons of the year, being able to read a spark plug with any kind of accuracy is impossible. If you were to run only straight AvGas then you would be able to read a plug like in the days of yesteryear.
On the up side of these modern times we now have wide band O2 sensors and the ability to read air/fuel ratios on a guage with far greater accuracy than what you can get by reading plugs. For example:

http://67-72chevytrucks.com/vboard/s...d.php?t=713728

[aerotest]

Those look perfect and the heat range is good too.

[trevarthan]

Originally Posted by HO455

Unfortunately in these modern times of ethanol gasoline, every brand having a different mix of additives, and the change in fuel mixtures for the different seasons of the year, being able to read a spark plug with any kind of accuracy is impossible. If you were to run only straight AvGas then you would be able to read a plug like in the days of yesteryear.
On the up side of these modern times we now have wide band O2 sensors and the ability to read air/fuel ratios on a guage with far greater accuracy than what you can get by reading plugs. For example:

http://67-72chevytrucks.com/vboard/s...d.php?t=713728

This is the first time I've heard anyone say this. Do you have any data to back up this claim? I'd like to know more.

[trevarthan]

Originally Posted by aerotest

Those look perfect and the heat range is good too.

Well, that's good news. But what does a truly lean plug look like then? Clearly I'm missing something.

[aerotest]

Lean will have some white dusting on it. Pre-detonation will have white spalding. It’s important to get the engine to temp, do a couple WoT pulls, and then read the plugs. Normal driving or a cold engine will lie to you. If you are really concerned I would buy a wide band O2 setup. It’s the definitive indicator.

[HO455]

Originally Posted by trevarthan

This is the first time I've heard anyone say this. Do you have any data to back up this claim? I'd like to know more.

I learned if from hanging out with Pat Usher who owned Sunset Engine Development. Smartest engine guy I've ever met. Here is a link to his web site. Read the Nerdletter #3. While he doesn't call out my statement in the article specifically, we have discussed fuel formulas more than once over the years. The article may lend some credence to my statement or you may just feel I'm full of it. It's all good.

https://www.cherylyoungonline.com/Pa...her/index.html

I should have mentioned in my original post that you can only only get the most basic idea of lean and rich from "reading" a spark plug. The difference between a 11:1 AFR and 16:1 AFR might be visible, but being able to discern between 13:1 and 14:1 would not be possible for most people. And since the arrival of the O2 sensor no one is bothering to learn what to look for so it truly is a lost art.

[Ironangel]

Your #1 plug looks perfect, the #3 is a tic lean...I've been reading plugs for almost 50 years now and is paramount if you raced and still ride the KZ-1000 Z1's...Try a WOT plug chop test by turning off the ignition at cruise speed and rolling to a stop in neutral...Those plugs don't look bad enough to melt holes in pistons...