Jerry Roberts Posted June 11, 2018 Report Share Posted June 11, 2018 Does anyone know why these spark plugs turn black on the insulator ? I am going to replace the plugs as they are three years old but I am wondering about the black . Is it from gases bypassing the steel part ? Quote Link to comment Share on other sites More sharing options...
HotRodTractor Posted June 11, 2018 Report Share Posted June 11, 2018 I've heard of/seen "corona stain" on spark plug insulators before - but that is usually brown or yellow and only a ring around the bottom of the insulator - sometimes you can see a glow around the insulator in complete darkness with the engine running - that is corona. I wonder if this is a similar result, but with a different color/effect from a newer insulator material... If it is, it doesn't mean much if anything. Interesting for sure. I'm in to find out if someone has a better idea to what this is. Always up for new information. Quote Link to comment Share on other sites More sharing options...
ggdad1951 Posted June 11, 2018 Report Share Posted June 11, 2018 does it rub off? Getting too hot? Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted June 11, 2018 Author Report Share Posted June 11, 2018 2 hours ago, ggdad1951 said: does it rub off? Getting too hot? Yes it rubs off like soot . The engine runs cool . Is the plug getting too hot ? ... not that I can tell . Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted June 12, 2018 Report Share Posted June 12, 2018 is there a metal cooper gasket under the plug and seating on the head? If the cooper gasket is missing or possible cracked this might cause the issue. Just a thought. Rich HArtung desoto1939@aol.com Quote Link to comment Share on other sites More sharing options...
Merle Coggins Posted June 12, 2018 Report Share Posted June 12, 2018 If it was leaking at the seat gasket there would also be soot in the cup area. Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted June 12, 2018 Author Report Share Posted June 12, 2018 No soot in the cup area and the copper gaskets are there . The engine runs fine at my low elevation of 14 feet but when I am up in the mountains at 6,000-7,000 feet pulling up hill it doesn't run too well . That is why I am changing the plugs . In the past the engine ran better in the mountains . Quote Link to comment Share on other sites More sharing options...
Mlindblom Posted June 18, 2020 Report Share Posted June 18, 2020 Did new plugs solve your soot problem? Mine are just starting to look like yours and I was starting to chase down possible causes? Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted June 18, 2020 Author Report Share Posted June 18, 2020 Well I changed the plugs quite a long time ago now and the new NGK s have a little soot but not bad like the old ones . I found that my vacuum advance diaphragm was torn and my coil was bad . All is good now . That pesky coil only acted up after it warmed up and only under heavy load . 1 Quote Link to comment Share on other sites More sharing options...
Jeff Balazs Posted June 18, 2020 Report Share Posted June 18, 2020 Fwiw I like the NGK BR 6S plugs in my truck. Heat range seems like it is spot on. I run them with a Pertronix module and matching coil. Even though I still have a 6V positive ground it starts like a 12V and never stumbles. Hth, Jeff 1 Quote Link to comment Share on other sites More sharing options...
DJ194950 Posted June 18, 2020 Report Share Posted June 18, 2020 Man checking prices on your favorite plug online are all over from $2 to $4. Ebay price seems to be lowest $15 for 6 shipped, from Maine, 5 day to Calif. from Maine-Not bad. $2 from NGK direct online but-shipping? Also works in some lawnmowers- - -? DJ Quote Link to comment Share on other sites More sharing options...
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