Plugs #1 and #6 carbon fouled

After some rough running and misfire yesterday, I took the plugs out for inspection. Plugs for the #1 and the #6 cylinders were carbon fouled. Cylinders 2-5 looked normal. What could cause the end plugs to foul? My thought was those plugs stay cooler, and not hot enough to burn off deposits. Perhaps I am running a little rich?

Howdy Back Nachoman

The #1 and 6 typically run a little lean due to distance from the centered carb and being farthest away. #3and #4 tend to run rich. So fouled is a bit of a mystery. And #1 may be cooler due to proximity to the water pump and the fan, while #6 can tend to run hotter.again, a bit off a mystery

What distributor? What brand plugs? What heat range? Any oil use issues? Are they oil fouled (darkish) or gas residue (whiteish) build-up?

I'd start with a set of new plugs gapped at .035" for a LoM ignition, or .050" for Ignitor and DS II and watch them closely.

Keep us posted on your progress on this little mystery.

adios, David

I'll throw out a couple of ideas?
How old are the plug wires?
Maybe worn valve guides letting a little oil in there?
Were they loose at all?
Sometimes my valve cover leaks and oil goes down into the spark plug hole.

These were motorcraft copper plugs. This is the centrifugal distributor with Pertronix I. Single barrel carburetor. I recently replaced the head gasket, and ran some seafoam through the engine to decarbon, but the plugs were cleaned afterwards. This was dry black soot, soft and crumbly that was white on the inside when I broke it off the plug. Distributor cap had some whitish deposits on some of the terminals. I mostly drive short trips, and have driven in quite a bit of rain lately.

Check for carbon tracking between the terminals of the distributor cap . You might want to go ahead and replace the cap .

Howdy Back:

How long were the plugs in? What were they gapped at? The short trips in rainy, cool weather suggests that the engine has been running rich due to the choke being on and never really getting to warm up temps for long. The question still remaining is why only the #1 & 6. What did the other plugs look like?

Carbon tracking in the distributor cap and/or leaking plug wires could be a factor, especially on #6. Check the inside of the cap. How old are the plug wires?

What heat range are the plugs? You may need a hotter plug considering weather and driving conditions.

Keep it coming.

Adios, David

Plugs - Motorcraft BF-32. New within a year. Wires also new within a year. Cap and rotor are probably about a year old.

The stock plug was BF 82 ,32 may be to cold ,but maybe they use a new plug number system.

I just checked the Autolite website and the 46 is listed as the stock plug.

I have 46's and haven't had to change plugs in years.
NKG WR5 is a good bet too.

Those specs are for a '78 Fairmont.

Yes I would run a autolite 46 or a motorcraft BF82 not a BF 32 too cold if mostly stock build.

Yes I would run a autolite 46 or a motorcraft BF82 not a BF 32 too cold if mostly stock build.

Well, I put some Autolite 46s in there that I had around, and it runs better. It still runs terrible for the first minute or so after cranking in the morning. Perhaps fuel boilover from the night before?

Regarding spark plug heat ranges - does anyone run different heat ranges for different cylinders?

Yes I run 1 range colder in nos 1&6, all plugs clean and light tan. Dropped my carb jet from a 56 to a 50, huge change.