Does anybody know what this yellow coloured plug means. Good, bad or OK? Ran for about 120 miles and as ambient temperature increased in afternoon started to get pinging under load going uphill but at normal cruise (most of the time) everything fine. Eventually pulled over & retarded timing a little. No more pinging. Two or three plugs are the same colour. Others nice tan colour but one was dry but no colour. I live in France and this is what is stated for the grade of fuel I use "Super Lead 98 (E5) is a mixture of hydrocarbons with an octane rating of 98%, giving it better resistance to self-ignition than Super Unleaded 95. It also contains up to 5% ethanol. It is intended for gasoline vehicles." Engine is a 327 sbc, small valve with Holley 600 cfm & Comp Cams XE262H-10 and dome top pistons.
It would be better to see a shot looking at the tip down into the porcelain, not to close though. Just looking at what you have that plug is lean. What brand and heat range is that plug ?
I think the yellow is sulfur, sometimes in the makeup of the steel itself or from fuel additives and on the rich side, is there a rotten egg odor? if 'yes', then rich.
Back in the leaded fuel days I think some if not all refiners added at least a bit of sulphur to their additive packages. Shell seemed to add more sulphur than other brands to their gas. If your fuel mixture was near the right range the spark plugs would take on a similar shade of yellow, even on the porcelin on the center electrode. When driven long enough to get the entire exhaust system hot clear to the end of the tailpipe (40 or 50 highway miles?) the inside of the pipe would also show a grayish tan coating from the lead. If your tailpipe tip was tan inside your fuel mileage was probably as good as it was likely to get. And sometimes there'd be a faint yellow coating. I've freaked out more than a couple strangers by asking them how long they'd been using Shell gasoline. Don't feel too bad about the removal of lead from your gas. Your exhaust lasts a lot longer without it.
Back in the leaded gas days I was pretty good at reading plugs. Now I'd have to get an up to date chart to be able to tell with the gas we have today.
Plugs are Champion RJ12YC which I think are near equivalents to ACDelco R45S but not sure. The gas in use is is known as SP98 E5 here in France and is of course "unleaded". My original post said "Super Lead" for some weird reason. I was thinking I was a bit lean and will richen a whisker. I originally set the two idle mixture screws using a vac. gauge after fitting a new Pertronix Flamethrower distributor and had to set timing the same way as my timing light is bust. Got highest vac on gauge and retarded timing about 1" Hg. I realise this can result in overtiming and hence, I was not suprised I got pinging under load. Plug is shown after retarding timing to stop pinging but might be still a bit overtimed as someone mentioned.
@Northerner , Do not know your Gas blend / Recipe, formula. Here gas off pump readings are misleading, By eye. Then when come to AFR thats a big Can of worms , #6 cylinder is leanest of the 8 Cyl 's . Beat to use O2 on 2,4,6,8 side , Ever better # 6 , Dual plane intake Mix's up the AFR On all Cyl's from Idle threw all Rpm's , This is where you get into stagger Jets, different heat Range on different cylinders,, when working for max power . Signal plane more controllable, Better Cleaner Long runners to Tunnel Rams . I think a Good Quality brand O2Gauger Would help & point fast results & I feel that the NGK are a better /superior choice Over Newer AC & definitely a Champion, @ least here in USA Gasoline /Petro Use there charts , the Lower # hotter plug Higher # colder , after the dash For instant This # is .750 reach Non - projected tip R5671A -"8 " Static compression 11:1 R5671A-"7" Static compression 10:1 & boost Up around 7 to 8- 1/2 boost. There is also chart's where to start on Heat range for static compression, Projected and non-projected recommendations , & ground strap designs , This is One of a Few Charts https://www.aquapulser.com/docs/NGKGuide.pdf
plug reading is one of the tools that can be used...if you look at all of them....with no idle on them that plug pictured looks lean and hot to me my biggest dividends have come from a trip to the wheel dyno
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