Aberrent Spark form the #3

Re: Aberrent Spark from the #3

To all,

Thanks for all the advice. I changed all four of the plugs to the taller Champion W16Y plugs. It has more than doubled the distance from the bronze wire to the spark advance linkage (3/8" to 7/8")

I have been driving the car in the same manner and trying to reproduce the aberrant spark. Here is a video of the same leaning procedure with the new plugs and no aberrant spark.

https://drive.google.com/file/d/1b40EuqUurFCd6qlJewkd4nvjHhC9PU7x/view?usp=drive_link

Now, I just have to figure out what heat range to use for the taller Champion plugs compared to the shorter AutoLite plugs.
3X -- heat range value of three (cold)
W16Y -- heat range value of sixteen(warm)
W18 -- heat range value of eighteen (hot)
And, also what gap to use. I used 0.035" for the AutoLite plugs. But, I have a 5.5:1 high compression head with chamber pressures at 89-92 psi in all four cylinders. Many have suggested narrowing the gap due to to the increase in resistance with the higher compression. I set the plugs in the above video at 0.030" and Blanche ran well.

Prior to changing the plugs...I mounted a GoPro phone underneath the cowl (thanks to the question from "Ed in Maine") and in night time driving there was NO aberrant sparks anywhere in normal driving and idling. No paint in the threads or boss, also. The only time I could get the aberrant spark was at the end of the carburetor draining procedure when the RPM was low (long dwell) and the mixture very lean (higher resistance in air at gap) -- like many have said.

I pulled all four plugs and three of them look the same as the one in the pic with "no carbon" -- greyish whiteish no blistering or fouling. Plug from cylinder #4 had some carbon and oil fouling.

I guess it was as simple as too short a plug.
Any suggestions on plugs: 1) reproduction 3X, 2) Champion W16Y (the "Y" means a projected plug, not sure what the projection covering the center electrode helps), or 3) W18?

I will try all three and try various gap settings and hopefully I can find a combination that works.

With much Gratitude,
Diastole in the Smokies.
 
Plug gap setting has a binary outcome – either the plug fires under load or it doesn't. The spec gap is designed to cover a lot of potential flaws – weak coil, bad gas, etc. If you have a nice strong coil and good plugs, you can set that gap at .035 or even .040. A longer gap, if fired successfully, helps the fuel burn more evenly. I always recommend setting plugs at the upper end of the range and then reduce the gap if and only if you get misfires.
 
I have the W16Y plugs and a Burtz high compression head. All four plugs have the correct color. The car runs great on these plugs. The gap is 0.035. The plugs are not too cold and not too hot. Sitting at the Goldilocks zone.
 
I have an older 5.2 head and run Motorcraft TT10 at 0.032". I tried W16Y and it did not seem to run as smoothly. TT10 are getting a bit harder to find, though, I get mine from the river store.
 
The system used by the model A did nothing to insulate the high tension voltage to the spark plugs. The aforementioned ways to apply insulation is the easiest way to guard against high tension flash over. A good induction coil can generate a high enough voltage to jump a half inch or more of gap. The old buzz box coil testers with the adjustable gap screw were calibrated to tell a person how good the coil was by increasing the gap during the test.
 
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