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.

[varmint]

Thanks for all the replies.
Got a compression tester and here's the steps I took:
1) left ignition off (no need to ground spark plug wires)
2) left fuel off
3) Lever from "High" to "Park"
4) plugs removed
5) throttle wide open
6) not concerned about generator (because it's not excited)
7) left cylinders dry
8) hand cranked to 30psi
9) electric starter to the finish number
Cylinders:1-2-3-4
44-47-43-44

To answer other comments:
ummm, yes, i advance the timing after it starts, quite a bit, like as shown in the manual
advance it more on magneto
did change the rich mixture to 1-3/8 turns
Repeat, if you missed it: "Also, it idles great, runs on battery, runs better on Magneto. Starts by starter or hand crank."
It's too late/too dark at night, so I did not start the engine. It will have to wait 'til morning.

[TXGOAT2]

Compression is OK. Fouled plugs will mis-fire under load. Cleaning them and gapping them should cure that. If the engine still runs irregularly under load, I'd check the timer and related wiring. It's not uncommon for the wiring at the timer to wear against the timer rod or the fan belt. Also be sure the choke is opening as it should.

[TXGOAT2]

My car starts easily with the carb adjustment open 1 turn. After it runs for half a minute or so, I reduce the adjustment to about 3/4 to 7/8 turn. I haven't had the plugs out of the engine in the last several thousand miles.

[varmint]

It runs on 1-3/8 turns. When I lean it in to 3/4 turns, it gets rough and 2-1/4 turns begins to sound different. Got it up to 20-25 on some empty city streets. Before I put it on a bigger road, it has some other issues to address. Drove it a mile this morning and a mile this evening. Getting used to stopping at stop signs is a challenge. The shakedown continues.

[Scott_Conger]

So you know:

your mystery of it "idling fine" and running horrible once the throttle was opened is due to the fact that at idle, the car is operating on the idle bypass circuit. The grossly maladjusted needle has some but not significant impact on the running of the car at idle (though I am surprised that it did in fact run at 6 turns open). Once the throttle is opened and vacuum drops, the primary path of air is now over the maladjusted jet and will flood an enormous amount of poorly atomized fuel into the intake manifold. This is the cause of the massive soot you found on your plugs. If you ran the car in this state for any amount of time, you may well find that the oil now smells of raw fuel and if so, is diluted to the point where you ought to change it.

Finally, if it takes nearly a full turn rich from "ideal" before it "begins to sound different", I would think that either the fuel level in the bowl is quite low or the mixture needle is malformed. A properly adjusted NH on an engine with no other ignition or vacuum problems should falter to the point of stalling when adjusted 1/2 turn lean from "ideal" and blubber and run decidedly worse around 1/2 or more turn rich from "ideal".

[varmint]

Scott,
I was going to start a new post but you entered the domain of the new problem.
I drove to a gas station and put three more gallons in the tank. This late afternoon I opened the sediment bulb valve and fuel began streaming from the carburetor. When I close the valve the streaming stops (good sediment valve). I have not yet pinpointed the problem but I'm sure that the extra pressure of gasoline in the cowl tank has something to do with it. You're the expert on this and will probably have the best steps to take. I've been digging for my carburetor manual and haven't found it yet, which is probably for a Holly NH center drain. I was going to look at receipts first to see exactly what parts I put in the thing. For all I know, it has the best needle yet the carb is unrebuildable.

[TXGOAT2]

Sounds like dirt.

[Scott_Conger]

Your float is not applying sufficient pressure to close the float valve. There may be dirt in the float valve keeping it open, the float may be binding on the side of the bowl or the tab on the float may not be shaped well enough to lift the float valve's needle high enough to shut off the fuel flow.

You don't have "extra pressure" in the cowl tank, but you do have "sufficient pressure", and it isn't enough to overwhelm a carb if the carb is clean and working properly

[speedytinc]

Improved T NH carbs had a larger than normal float to work with the extra head pressure.
Maybe a contributing factor, although a lot of improved T's out there are running satisfactorily with the earlier float.

[Scott_Conger]

the larger float came about to solve rich running on rough roads. I think our driving environments are such that the smaller float suffices fine in most circumstances. Most people don't know/care/need the thicker float, but when it is needed, it is needed. I suspect that the Oregon folks who do a lot of off-roading in "T"s either have, or could use the extra large float, for instance.

Additionally, the improperly designed float valves sold by most vendors have such a tiny through-hole that this naturally reduces the effective head pressure gained by cowl mounted tanks and thereby naturally reduces the need for the extra buoyancy the larger float gives. This is primarily why most folks with Improved Fords don't see a need for the thicker floats...they are already suffering from restricted fuel flow in the first place.

Edit: attachment added -

[RajoRacer]

The several "larger" floats I've ever recovered were from Vaporizer carburetors - never removed one from an NH.

[varmint]

Before I take anything apart, I allowed the carburetor to dry and then ran two short videos while I opened the sediment valve. Here is before and after photos:

fuelish 01.jpg (91.08 KiB) Viewed 283 times

fuelish 02.jpg (83.88 KiB) Viewed 283 times

fuelish 03.jpg (54.71 KiB) Viewed 283 times

[RajoRacer]

Thanks Scott - that is informational !

[Scott_Conger]

Steve

you're welcome.
I try to be careful to limit my advice to things that I have actually done/experienced, or are linked to historical documentation
Speculation is a area covered by plenty of others

[varmint]

What I found tonight:

Cleaned out the sediment bowl - found a little debris.
Cleaned out the carb bowl - found a little debris.
Does not have the larger T-6333-B.
Float needle seems to be almost buried above the surface.
Tang on float was not making contact with needle anymore.

[varmint]

In case someone missed it, the carburetor has a "NH" tag on it yet there is what appears to be a "G" steel needle. I checked my email receipts from years ago and packing lists. All I see if stuff purchased for "NH" but I don't even see that part number listed in my records anywhere. So, I think it must have come with the Holly, and that is why it was sold to begin with. Maybe I'm wrong, that this is the correct part but I certainly knew next to nothing back then. Anyway, I ordered the 6210 and 6212 this morning, and gaskets.