06-14-2019, 05:43 PM | #1 |
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Location: Chattanooga TN
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Spark Plug reading
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! |
06-14-2019, 05:51 PM | #2 |
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Re: Spark Plug reading
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.
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06-14-2019, 07:10 PM | #3 |
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Re: Spark Plug reading
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
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06-14-2019, 09:31 PM | #4 |
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Re: Spark Plug reading
Those look perfect and the heat range is good too.
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1969 C10 Suburban Custom (Factory 396/TH400, survivor with no rust) |
06-15-2019, 10:08 AM | #5 | |
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Re: Spark Plug reading
Quote:
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06-15-2019, 10:12 AM | #6 |
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Re: Spark Plug reading
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06-18-2019, 08:17 PM | #7 |
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Re: Spark Plug reading
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.
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1969 C10 Suburban Custom (Factory 396/TH400, survivor with no rust) |
06-19-2019, 10:44 PM | #8 | |
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Re: Spark Plug reading
Quote:
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.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F2 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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06-20-2019, 10:21 AM | #9 |
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Location: Falls City, Nebraska "100 Miles From Nowhere"
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Re: Spark Plug reading
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...
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