What do these plugs tell you?

I've been noticing an occasional missfire and slightly rough running at idle over the past week and a half or so, so today I pulled a few plugs out to see what they look like. These plugs only have about 10k on them, and I was unpleasantly surprised at what they look like, I usually like to get about 20-25k out of a set of plugs, but these will need changed immediately. The plug pictured below is from cylinder 3, and has a heavy tan colored buildup on the ground strap. The center electrode is also pretty badly worn, though that is somewhat common with the MSD 6A ignition. It almost looks like the gap has closed up even as the electrode has worn down? I set the gap at .045 when I put these plugs in just to experiment around, I usually run 0.55. Sorry, the pic is the best my cell phone can do.



I wasn't able to get a good pic of the plug out of cylinder 1, but it was really bad. It had a lot of build up on the ground strap, and the center electrode had completely worn down INSIDE the porcelain.. I've never seen anything like that before. These are Autolite 46 plugs in a '71 200 with MSD 6Al ignition, Duraspark II distributor, Rochester BC carb, and a header. The fuel mixture seems to be pretty good, maybe slightly lean, I'm just stumped as to why there is so much buildup on the plugs, and the electrodes wore so much in such a short amount of time. Usually when I change plugs with over twice the mileage these have in this car, they are pretty clean, just the electrodes are worn out. For now I'm going to throw a set of Motorcraft plugs in it and go back to the .055 gap. This car is a daily driver and sees about 70 miles a day on the interstate, anywhere from 2800-3500 RPM about 85% of the time it's running.

 

Jamie; looks like it is burning a bit lean. Fatten it up a bit, and it should be good!

 

It looks overheated to me, with a little preignition. More fuel, maybe a little less timing. Check for a leaking intake manifold or cracks. Also check that thoes plugs are proper for the msd setup. If your using the same type of plug that the old points setup used, you may be over powering them. Try a plug made to handle the msd ignition. Good luck.

 

Jamie,that is ash deposits on your plug it isnt lean or overheated ash deposits are usually caused by the car burning oil probly from worn valve guides or seal. It could also be caused by certain fuel blends and fuel additives.

Hope this helps ya