Carbon on porcelin of plugs,flathead V8
 

My 46 Ford JUST getting for road ,most running time spent on short test runs of mile or 2 and abit of idle run time. Plugs seem to have carbon on the porcelin and a few plugs fouled now. Plugs are all tight. What causes the darkening on the porcelin? Perhaps this was caused by heat? Thanks

Re: Carbon on porcelin of plugs,flathead V8
 

I'm guessing you mean on the engine side. Short runs will build up more so, then when you are running it up to temp. Fouling is usually a rich mix. Best is a brown plug but to be honest I don't ever see one. But if it never leaves the driveway, that won't help. I'm not bashing, as I don't run around the country putting 1ks on my flatheads every week.

Re: Carbon on porcelin of plugs,flathead V8
 

I recently had a fan belt issue and that resulted in black deposits all over the exterior porcelain.

Interior porcelain will be mixture related

Re: Carbon on porcelin of plugs,flathead V8
 

Think you need to clarify what you are referring to, saying porcelain might indicate the part of the spark plug that the wire connects to. If you are referring to inside the combustion chamber it can be an overly rich mixture, too cold a spark plug range or not running the engine hard enough or a combination. Babying an engine if often not a good thing, especially if it is a new build.

You might start by posting what type and the heat range of the plugs you are using and what the jetting is on the carb(s).

Re: Carbon on porcelin of plugs,flathead V8
 

So undoubtedly some choke-on time? short trips, idling with rich mixture will blacken plugs. If a fresh rebuild, rings may not be seated yet, short runs won't help that.

Re: Carbon on porcelin of plugs,flathead V8
 

Bump the heat range a couple ranges . But short trip will cause your problem

Re: Carbon on porcelin of plugs,flathead V8
 

A picture of the spark plug, would be a great help.

Dark and sooty would probably mean to much time spent, with the choke on, with your short run driving.

You really need to get it on the road, for at least 10 miles, at 55+ mph and then check your plugs, to know what the basic plug/engine condition is.