Factory *spark gap* Low vs. High head

[varmint]

This question is about the different spark plug gaps for according to Henry for the low compression head verses the high compression head that he manufactured.

FAQs
Why? I'm resolving a poor performance running issue with our T. It only goes 10mph in low and 15mph in high.
It has stock ignition,
New coils from the coil doctor,
New wires,
Fresh gasoline - no ethanol,
No distributor, nor do I ever plan on installing one.
Factory engine, High head - improved Coupe
New Day Timer
All coils are buzzing.
Champion X plugs

I planned on doing a compression test and pulled the plugs:

I found carbon fouled plugs, gapped to .025"
The Manual says 30/1000" or 1/32" (.03125")
Champion X says .025"
Somehow the lean-rich mixture was set to 6 turns open.

The compression gauge itself, does not hold pressure any more. So I plan on replacing it. My understanding is that opening the gap will help reduce carbon fouling and that I should gap the plugs to how they work on my T. I set the mixture to 3 turns open and changed the spark plug gap to .031", then reassembled everything that was undone. I probably won't be able to test it again until Thursday night.

There is on nagging question, having read 1/2 dozen forum posts about gap, shouldn't Ford have published different gaps for the two different compression heads they he produced?

[Kenny Edmondson]

Most mixture screws settings are around 1 1/8 turns open on NH and Simmons carbs. You mentioned everything but what carb your running. “Improve Coupe” could be a vaporizer though… and that would be some different issue possibilities.

You need to check and set your initial timing making sure the advance lever is all the way up and the ignition switch is on battery with the number 1 plug removed, crank the engine over slowly with the hand crank and the #1 coil should start buzzing as soon as the piston starts downward.
Make sure you are running on mag. Make sure your running plenty of advance (the advance lever 3/4 or more down). No premium gasoline. I run champion X’s at .028.

I don’t think you have a compression or intake gasket issue since all the plugs are burning the same.

Let me know what you find.

[George House]

Vern,.. It doesn’t appear to me that your spark plug gap is the cause for your stated T poor performance. Judging by the ‘business end’ photo of the spark plugs, they’re WAY TOO SOOTY’. May I assume they became that way by your stated 6 open revolutions of the fuel/air needle ? Even the adjusted 3 open turns of that mixture needle might be a tad rich. Try 1 1/2 open and adjust it by ear….

[varmint]

Never saw evidence of a vaporizer. It came with this Kingston L4. I thought the tag on the back side said "NH" so I purchased a replacement Holly NH and replaced the parts in it some years ago. Yes, the air/fuel needle on top. OK will open to 1-1/8 to 1-1/2 turns instead.

Also, it idles great, runs on battery, runs better on Magneto. Starts by starter or hand crank.

[ModelTWoods]

Vernon, i don't think I'll get any disagreement from forum members on the fact that Ford basically made the low head (with compression at or slightly above 4 to 1) and the high head (with compression normally at 3.98 to 1. Aftermarket heads with higher compression were available, but Ford never mad a "high" compression head, and there is so little difference in compression between Ford's low and high head that it shouldn't have any effect on spark plug gap or the fouling of plugs. Other problems cause those things.

[TXGOAT2]

A plug gap of .026 to .032 is fine. A smaller gap may give easier starting with a weak magneto. Your plugs show that the engine is running WAY TOO RICH and the plugs are heavily soot-fouled. Clean the plugs thoroughly and set the gaps to .028. Make sure the float level in the carburetor is correct, then seat the adjustment needle gently, and then open it one full turn. Start the engine, set the throttle for about 600 RPM and advance the timing about halfway. Drive away. After a two to 3 minutes, adjust the carburetor about 1/8 to 1/4 turn leaner. Advance the timing as the situation demands. Under most conditions, you should be able to shift to high at 6 to 8 MPH, and stay in high from then on unless you have to stop. The car will not lurch or buck when shifted to high if it is running as it should and the shift is handled as it should be.

[Norman Kling]

When you adjust the mixture, turn the needle clockwise until it begins to run rough. Then counter clockwise till it begins to surge. somewhere between those two adjustments, you will find the spot where it runs the smoothest. Leave it at that "sweet spot". It might need to be opened a bit to keep from stalling when cold, but as soon as it begins to warm up, turn it to the sweet spot.
Norm

[Moxie26]

When he gets a better compression tester, he'll find out if the rings or valves are the culprits in a lower compression

[NoelChico]

I see no mention of timing, running on battery vs magneto, or advancing the spark after the engine is running.

[TXGOAT2]

"Somehow the lean-rich mixture was set to 6 turns open...."


Running WAY TOO RICH. You can test compression using the hand crank.