Unkown plug condition

[dbeardslee]

I've been having my issues lately since rejetting the old girl for pods. During the process the valves were found to be in need of adjustment (which I did) and I also found a vacuum leak at the carb boots (also fixed). I diddled around with float heights, pilot jets, and mixture settings until I finally have her running strong through the entire rpm range. During the process the plugs got pretty foulyfied several times and I cleaned them and continued to march. Yesterday after a low rpm putt-putt I pulled the plugs, and I have never seen this condition before - the sides of the insulators were deep brown, but the very end of the insulators was almost as orange as an extension cord. There was a little soot on the end of the plugs (to be expected when running in that low rpm range of 2-3K) but nothing on the electrodes - just that weird orange ring. Anybody know what this indicates?

[oseaghdha]

Could be something in the fuel, maybe an additive.

[dbeardslee]

You may have something with the fuel. I often run 87 octane gas, but after the adjusting the valve clearance I'm sure the compression is up where it's supposed to be. Could that be an indication of pre-ignition? I gassed up last night with 93 octane, so we'll see. I also run a little acetone in the gas, but I've been doing that for some time without this coloration.

[oseaghdha]

Like this?

APPEARANCE: Spark plugs fouled by MMT (Methycyclopentadienyl Maganese Tricarbonyl) have reddish, rusty appearance on the insulator and side electrode.

[dbeardslee]

The picture shows a much more severe case, but that sure looks like my mystery color. That last tank of gas came from BP rather than my usual Shell fill-up. I gassed up at Shell last night and ran the old girl on the highway, and this morning the plugs look perfectly clean. I'm thinking it was probably a combination of the gas and the low rpm riding. Thanks for the link, Dan.