Spark Plug Reading 101

Can you tell me what you think? Hard to get a good picture but it appears to be running a tad rich since I cleaned the injector in this case. I am replacing all of the injectors and at that time will be adjusting the mixture. I didn't run the car much , say 20 miles.
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I recently replaced the cam gasket...perhaps it's not sealing properly? How does the tip look?

 

From that photo, you can't tell too much, but it looks like you've got a little oil and it's rich. I'd lean it out a bit, then get another look. Remember, you have to shut off the ignition while under full throttle in the higher rpm range for this "plug chop" to tell you anything useful.

Art

 

Heres one from the same bank...opposite cylinder [#1], the other is #4 and I do have a leak below the dizzy in that area. Thsi is an older 308 2V motor

Sorry...I posted this before you responded. I shut the motor down at idle
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Yep...a bit of residue on the top of that cylinder too.

 

Well, I cleaned the oil off of the threads and put the plug back in nice and tight. Took the car out and drove it till nice and hot, up and down the rpm range. Shut her down at WOT and here's the result [BTW, no sign of oil on the treads].
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That looks very healthy to me. Nice golden tan color

 

Yes...I know this is one cylinder I need to watch but I am happy with the tip. I am changing over to new injectors so I will be re adjusting the mix at that time.

 

I think if you are really serious about reading the plugs it's probably best to do with a fairly new set. No tell what bad gas and other variables including age. Put in the new set and drive it for a bit and then read them.

Here is a great pic of a plug with some of the metal cut away to show the proclean and the dark ring described earlier. The higher the ring is on the porclean the richer the car is running. This one is about right.

BTW Great thread, I learned this stuff just a couple years ago. Shocking to find out everything I ever thought I knew about reading spark plugs was wrong. I blame it on that Champion poster that every shop in America had on the wall showing pictures of plugs.
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I find that my '76 308 plugs get a bit loaded up and dark looking when I take the car out and not run it hard. The jets are set fairly rich so the car needs to run hard to keep the plugs clean. Once I take it out and run it hard, all is right in the world and the plugs look perfect. Run them hard and keep them serviced is the key IMO

 

I'd lean it out a little, put new plugs in, get a good plug chop, and see what you've got. There are some signs of detonation on the plug, but I'm unsure if that is recent, or maybe bad gas sometime in the past. Best way is to check it out.

Art

 

It is a fresh set of plugs. Once I am done with the injectors and mixture I will change over to irridium plugs.

 

I had run some octane booster thru the tank recently and it may be residual...they were almost orange at that point before I changed to fresh plugs.

 

Just spotted this thread via No Doubt's signature in a Vintage thread.

I used to stop by Lar's shop when passing by enroute to Pecan Island, Louisiana; small operation, but big results.

Funny to see his name mentioned here.

 

Someone mentioned the wet oil on the plugs. This usually happens at idle or slow speed when the vacuum is high and the engine can suck oil past the valve seals or even the rings. Notice when he did the plug cut there was no oil.

 

Thank you there is some great info here

 

Up for analysis is a pic of how my spark plugs look in the 308. everything looks great except for the black ring at the bottom of the threads – which would normally indicate a rich mixture. Although the A/F mixture at the dyno indicates a spot on mixture at WOT. I pulled this plug just after a spirited run up the canyon and shut the car off immediately after a WOT jaunt. Please read the following: I have an after market electromotive ignition, and I also replaced the carburetors with a TWM injection system with the electromotive tec GT ECU. The limitations on the ECU along with no cam sensor prohibit pure sequential injection. Hence, I get a ‘waste’ shot of fuel along with a waste spark. Ie: one cylinder fires on the compression stroke and the opposing cylinder gets a waste spark and a waste shot of fuel on the exhaust stroke. I believe this is what is turning my plug dark at the base. As far as driveability, the car runs and idles great – gas mileage is an average of 10MPG. I have a pyrometer in the exhaust header and with this system I noticed I am running cooler than with the old system (carbs) – most likely due to the waste shot of fuel. So, the bottom line is, I am not sure what to believe. Am I getting fooled by the A/F reading at the dyno because of the waste shot of fuel? Am I running too rich based on the color of the base of the plug (just after the threads)? Or am I OK. I am running NGK BP5ES, BP6ES were too cold (most likely due to the extra shot of fuel I believe). Thanks folks!
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I just got an Innovate Motorsports LM-2. I'ts a wide band O2 sensor that can data log. I'm putting it in the racecar along with a TPS on the Holley style carb and reading the RPMs. After each session I can download the data into the laptop and watch the O2 sensor readings and see what RPM and throttle positions they were at. Just arrived today, hopefully get some good data at PVGP at Beaver Run this weekend. Engine builder told me to read the plugs at WOT and go back and look at what the O2 sensor read and use that number for a baseline not to just trust the O2 sensors. I have a pretty steep learning curve ahead of me in the next couple days.

 

Ok, so learning about plugs here.

Im confused. Post #1 and posts #8/9 seem to be contradicting to me. In #1 it states that the plug temp can be read from the strap. In posts 8/9 it is stated that the strap indicates timing and that the plug temp is read from the number of discolored threads.

Which is correct? Are they both correct?

thanks,
Aaron

 

Spark plug reading has to do with performance of the combustion chamber so it must be an assessment of engine's health. Complication arises if you ever saw (and probably did see) the engine of drag racing cars blown-up. I do look at the link provided in the OP and I wouldn't say an engine on steriods matches my thoughts of health.