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By RossL - 2 days ago
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I changed spark plugs last week. After 150 miles I checked them, they we totally white. I increased my main jets from 50 to 53. This is what they looked like after 200 miles with the 53 jets. I increased the jets to 55. How long should I wait to see if they are still white, or hopefully tan? The car is running really well, except for hot water temps when the AC is on and I'm doing 75/80 MPH for 15 minutes
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By KULTULZ - 2 days ago
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SPARK PLUGS – AUTO-LITE I am slowly moving away from Auto lite to NGK on the shop-built engines due to having a better heat range selection with NGK’s as well as having some brand new Auto-lites not firing from the git go. The Auto-lites have been coming from both Mexico and China, but it is the China made Auto lite spark plugs that I have had trouble with. It seems to be potluck at the parts store on which country of origin the Auto-lite spark plugs are from. I now do a mandatory ohm check on the new spark plugs before installing them.
TED EATON - http://forums.y-blocksforever.com/Topic165607-3.aspx |
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By Joe-JDC - 2 days ago
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If you are using ethanol mixed fuel, then you may need to jet up another 3-4 jet sizes. Joe-JDC
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By Deyomatic - 2 days ago
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Look for videos on YouTube where they cut the spark plug so that you can just see the inner insulator. They say that is the best way to figure out if you're rich or lean.
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By Ted - 2 days ago
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I do not use the inner porcelain of the spark plug for fuel mixture adjustments. Coloring of the porcelain simply takes too long and especially with ethanol laden fuels. I look at the outer ring where the strap attaches for mixture adjustments. I do look at the porcelain with a magnifier for signs of detonation and excess oil in the combustion. I look at the threads for the heat range yours do look to be on the cold side.
Other comments always welcome.
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By RossL - Yesterday
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Ted (6/9/2026)
I do not use the inner porcelain of the spark plug for fuel mixture adjustments. Coloring of the porcelain simply takes too long and especially with ethanol laden fuels. I look at the outer ring where the strap attaches for mixture adjustments. I do look at the porcelain with a magnifier for signs of detonation and excess oil in the combustion. I look at the threads for the heat range yours do look to be on the cold side.
Other comments always welcome.
I guess I need some sort of AFR gauge to see if I'm jetted correctly. I may go back a couple of jet sizes for now.
Could you expand on this statement " I look at the threads for the heat range yours do look to be on the cold side." Not sure what you are looking at, are you saying it's too rich or lean?
Does this tell you any more? 
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By DANIEL TINDER - Yesterday
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Back in the day, the way we gauged jetting from porcelain color, was to shut down during an extended full throttle run, and THEN pull & examine the plugs.
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By Ted - Yesterday
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For the spark plug heat range, I am looking at the color change at the threads. I consider the spark plug heat range to be about right when the color change occurs at two threads in from the bottom of the plug. If the color change is occurring at three threads in or more, then the plug is running on the hot side. Your plug on the right side of the original picture looked to be wet or not burning completely at the threads which would put it on the cold side. Maybe that’s the result of some excessive idle time before removing the plug? The left side plug looks much better. Don’t confuse oil or wetness on the threads for a heat color change. I am looking at a picture so I could very easily be wrong on this one. Autolite 45’s are colder than the Autolite 46’s and yours do look to be 45’s.
Looking at the last picture you posted and based on the wet appearance of the outer ring, I’m going to say you are rich. If it rubs off easily with a swipe of your finger, rich it is. Before the days of the wide band and A/F sensors, spark plug readings did get us to where we needed to go.
For the timing, I look at the color change in the strap. In the middle of the bend is always a good target for that. The color change being closer to where the strap attaches to the spark plug outer indicates too much timing and closer to the end of the strap or center of the plug is not enough.
Other comments always welcome.
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