Does anybody tryed this ? (spark plug reading)

[georgesgiralt]

Hello,
A while back, here, I got this link : http://www.4secondsflat.com/Spark_plug_reading.html
This Sunday, I went for a long ride (250 km) without a stop. So I could give it a try.
I wonder if this is applicable to our plugs ? Because I can't find the "timing marks" the plug should have, and I am dubious about the whole thing altogether...
So I would like to get other's advice about this.
(BTW my actual plugs are NOS Champion N6Y less than 3000 km old)
Thanks in advance !  

[Luca]

Wow!  There is a lot going on with those plugs!

Since those people are tracking their cars, I imagine the engines are running under pretty consistent conditions.  Might make the whole advance thing difficult to see on a street vehicle.

Oil on the plug is an easy way to see if you are leaking oil internally.  It doesn't always make the exhaust very smoky.

I find that the plug color can be a good indication of the mixture, mostly at idle if you aren't doing performance mods and can trust your jetting (you cut the engine at the RPM you want to read the plugs at).  I don't read plugs to do a final tune, but it can help get an engine running (perhaps setting idle mixture on a 4 cylinder engine if you don't know how far to unscrew the idle mixture screws).  And some anecdotal proof that plug color works:  my brother has a Ford Falcon with a single carb and straight six engine.  The front and back cylinders (farthest from the carb) run a bit leaner than the four inside cylinders and you can see that in the plugs.

You shouldn't have to mess with plug temperature unless you want to improve the performance of the engine.  Most agree the best way to do that is buy another motorcycle

[Barry]

I find the whole thing about reading plugs interesting but in practice I think it's mostly applicable to the full bore acceleration runs that the web site is talking about. I think it's useful to us for an indication of gross mixture problems and perhaps to compare plugs side to side. First thing to accept is that the base ring is going to be black to a greater or lesser degree as the plug body is at the same temperature as the cylinder head and since when did they not get a coating of carbon. The extent to which carbon builds up will tell you something. In the same way I also think you can judge something about the mixture from the piston top which again is always going to have a carbon coating but if it's thin that tells you the mixture is not excessively rich.

[Air4Life]

FWIW: I definitely saw the timing marks on both ground straps, along with the porcelain indications.  The plugs I examined may very well have been the originals, just prior to me replacing them.  (~43K miles 1983)