Should I use a colder plug?

[Reiver]

Originally Posted by Jerome74911S

More likely an air leak, as the engine tends to run rich overall. Are you referring with these comments to the picture just above, or the original 2 pictures of the same plug in the original post?

The top photo's...your 'bad' plug looks normal on the top pic side and not so good in the second shot other side.....un even combustion for some reason that'll take some looking into.
I would like to see, if it were my ride, what a clean plug looked like under load. Quiet highway 70 mph run achieved under load then cut the engine and pull the plug roadside.....that's what we use to do when I was a kid tuning hot rods.

[Jerome74911S]

Originally Posted by HawgRyder

When I was running a drag car (427 Ford Fairlane) I ended up with 3 different manufacturers of plugs...in a couple of different heat ranges.
It made about 2/10's of a second better times with that combo.
I know...a V8...but the basic principal is the same....use what works for you!
Every engine has hotter and cooler running cylinders...it's the cooling system that causes that.
If you put slightly cooler plugs in a hot running cylinder...and hotter plugs in a better cooled one....the result is a smoother running engine.
There are many people that will deride this idea...but in my experience...you do what needs to be done to get the job done.
Bob

Now this is interesting. Actually, I thought yesterday that I should run out and check to see if the suspicious plug was of a different heat range than the rest, by some accident, and that this could be a cause of it looking different from the rest. That's a long shot, though.

Your idea, to run different heat ranges - or even different makes - of plugs is intriguing. People have mentioned that the plug could be too hot, or not hot enough. I guess I'll experiment both ways - after I check for vacuum leaks, again . . .