Sooty Spark Plugs ????
 

Just did a 1,000 mile compression check on my rebuilt engine... all cylinders were 70#....Which I believe is "good"... the spark plugs hall had a thin film of carbon on them, though the very tip of the electrode had grey-white ash (Hopefully my photos get attached?) .... does this sound normal... if not can you make suggestions.

The spark plug gap was .027, I typically drive with the GAV valve turned to the left about a quarter turn and of course the advance lever down to the floor...

Thanks for your collective expertise....

Re: Sooty Spark Plugs ????
 

Personally, I would change to the Original style deep reach Champion 3X plug & set the gap at .35. I think you will get better gas mileage & a little more power..

Re: Sooty Spark Plugs ????
 

Hallo Indy, it looks to me as if the spark plugs burn clean, but before screwing out the engine for some time left with idle speed?

The sparking plug face is not bad.

Re: Sooty Spark Plugs ????
 

Good question. Did it idle a while before you checked?

I really like the 3X as well. It does reach deeper into the chamber like ford designed it. I agree you’re gapped to tight.

Re: Sooty Spark Plugs ????
 

If it runs OK with the GAV all the way closed after warm up, I would run it that way for a while and recheck the plugs. The gap needs to be set a bit wider also.

Re: Sooty Spark Plugs ????
 

The spark advance should typically be no more than half of the way down. Fully down is too much advance.

Re: Sooty Spark Plugs ????
 

Yes too much for slow or hilly travel but not too much speeding down the highway if the timing is correct. Adjust as needed!

Re: Sooty Spark Plugs ????
 

Thanks for all the great responses... Yes, it idles very well; No, I only have the advance all the way down on long level roads (which are very common in Hoosier Land)... will look into increasing the plug gap....I guess it is unrealistic to see a Model A spark plug with white ash around the electrode as you see in modern gas engines ???

Thanks again....

Re: Sooty Spark Plugs ????
 

I think your plugs are a bit sooty, probably because you are running too rich.
Or, possibly you plugs are too cold running to burn off deposits.? You do not say what brand and grade they are.
I am running Champion W16Y in two higher compression engines. Both run just slightly tan colour on insulators, grayish on earth electrode and black on bodies.
This is with GAV valves about 1/3 rd turn open. At 1/4 turn they burn almost white insulators. This did cause exhaust valves to almost burn at sustained high speeds many years ago, and since running at a very light tan colour I have had no more trouble for 30000 miles or so.
Where your GAV needs to be set depends on the flow rates of your particular jets.
To assess running mixture you need a mile or so of sustained running and then immediately cut the motor, clutch pedal down and cruise to a stop in neutral. Remove and exami e the plugs.
Otherwise, if you idle first for more than just a few seconds you will be reading idle mixture, not running mixture.
Recently we pulled the plugs of several members cars after a running through the mountains and they looked just a bit richer than mine, but still with a light tan colour on the insulators. Some were Motorcraft plugs, TT100 I think, and some were Autolite brand.
From the above I think too lean and white risks burnt valves, but the Model A should run with tan coloured insulators and clean earth electrodes. The ends of the bodies do seem to run black, but crisp dry carbon not fluffy or oily.
SAJ in NZ

Re: Sooty Spark Plugs ????
 

Kinda surprised nobody pointed a finger at carburetor jets or is that a non sequitur at high speeds?

Re: Sooty Spark Plugs ????
 

Ericr. That is what I was referring to where I said "where your GAV needs to be set depends on the flow rates of your particular jets".
Running mixture is governed by main and compensating jet flow rates etc, , with fine tuning by the GAV setting depending on altitude, petrol quality, air cleaner restriction etc etc.
If closing the GAV right down does not result in a lean-enough mixture, then jets need recalibrating by replacement, soldering up and re drilling etc.
SAJ in NZ

Re: Sooty Spark Plugs ????
 

I do not see mention if good procedure was followed. If he pulled the plugs after running cold or idling for a short period, this may not give you a good plug read.


I prefer to put in a fresh set of plugs, go driving at med to faster speed for an hour or 2, push the clutch in and turn off the ignition. Coast to a stop and pull the plugs.

Re: Sooty Spark Plugs ????
 

That is right. But it is not necesary, to take new spark plugs. The old mounted plugs burn free after 10 miles strong drive.