Ford Flathead AFR Gauge Anomalies

[glennpm]

I started this thread on HAMB, https://www.jalopyjournal.com/forum/...alies.1337799/, and got a few replies but nothing since Friday so excuse me for asking here too.

I just finished installing an AEM 30-4110NS wideband UEGO gauge but the AFR readings are off.

- 268 CI 59AB block
- 4" Merc crank
- 0.400 Offenhauser heads
- Isky Max 1 cam
- Dual Stromberg 97s with .044 jets (stock .045) which operate at close to sea level
- Real Bosch 017025 sensor
- Power valve sizes, don't know yet
- Accelerator pump rod is in the Summer position
- 97 Heaven rebuilt these two carbs years ago for me and have around 2,000 miles or so on them
- Floats set correctly
- Drive at around sea level or so
- Pic of air cleaners used below
- Fuel pressure is ~2.5psi

The reason for installing the AFR AEM gauge was to see where I'm at. Car runs well, required choke to start at all times and I thought I could be running lean.

- At idle ~1K or so, the AFR is about 13.5- 14.whatever
- As soon as I give it ANY gas on the road, APRs are at or slightly above 10
- Plug color looks decent. Pics taken this morning below

Given that the power valves activate at half throttle or so, not sure if these could be a problem.

Artificial intelligence take:
"The Stromberg 97 carburetor typically comes with a Number 65 power valve for sea level use, but the appropriate size can vary depending on the specific application and fuel requirements.
For dual Stromberg 97 carburetors, it is common to use a Number 65 power valve, as seen in some installations where the setup involves multiple carburetors."

From Uncle Max, re. dual 97s:
https://www.jalopyjournal.com/forum/...t-jets.419923/
"I don't believe in adjustable jets. (where's the baseline?)
I do believe in marrying the right jets with the right powervalves, remembering that a properly functioning powervalve starts to enrich the mixture at about 1/2 throttle - due to the "hydraulic" action of the accelerator pump, and becomes fully open at the end of the stroke. I also believe, for your flathead, assuming your're not planning to do much driving in the Andes or Himilayas, the best choice is .043 mains & number 69 powervalves. Set it and forget it.
No Strombergs were killed or injured during this post. . ." :-)

[38 coupe]

I would definitely take Uncle Max's suggestions over AI.

I have an O2 sensor that I set up to be portable with a tail pipe clamp so I can use it on different cars. It has been years since I used it on the 37 sedan, stock engine with a single 97. I remember being surprised at how rich the readings were, but how good the plugs looked. I did adjust the ignition timing slightly, and found that affected the O2 readings as well, you could try that.

The 38 has an identical 21 stud engine to the one in the 37, except a Chandler Groves carburetor instead of a Stromberg 97. I have checked the ratio on the 38 , and it was a much cleaner reading than the 97 was. When I built the carburetor for the 38 I used the O2 meter to check operations since I used parts from three or four different carburetors to make one. I remember increasing the jet sizes from 48 to 50 or 51 to get out of the lean range. For single carburetor use I prefer the later Chandler Groves / Ford / Holley 94 style since I find they have a more consistent ratio over the driving range of the engine. I haven't played with running two carburetors so I have nothing to offer there. I think the Chandler Groves gives better fuel economy for the same feel of power when driving.

I thing the alcohol in today's pump fuel makes plugs look good over a much wider range of ratios than was true decades ago when plug reading was an art form. If it runs well, and gets acceptable mileage, don't fix what ain't broke.

[glennpm]

Hi Fred,

Yes, I'm surprised that the AFR is showing so rich and the plugs don't. I like your take on it, "I think the alcohol in today's pump fuel makes plugs look good ..."

I'm running 7° advanced. Engine starts well, choked. My gas mileage of 13 to 15 or so is not the best either.

I wrote to Max this morning regarding his quote above and most likely will try jets and PV changes toward a leaner configuration. I'm not good at leaving good enough alone and will probably break it until I fix back to what I started with :-)

Glenn

[Bored&Stroked]

I'd follow the advice of Uncle Max. Where do you have your O2 sensors mounted and are you sure there are no upstream leaks - like with "slip on" extension pipes and u-clamps?

You have to make sure that the system is 100% sealed - before your O2 mounting location.

Plugs: It is really hard to read plugs these days - the fuels burn so clean that it is rare to see chocolate coloring like in the "old days". Trust what the AFR gauge is telling you and make sure your timing is correct. Obviously, you don't want to be too lean or too advanced and cause detonation. I'd shoot for 24 degrees of total advance (around 2000 rpm or so).

97s: I've found they tend to run a bit rich when under heavy load (power valves open). I would do a few road tests ---> partial/normal acceleration vs putting your foot into it. Mine tend to dip down into the high 11's or 12's under heavy load.

Shits and Giggles: You might also run your road tests both with and without those air-cleaners. You'll probably find they make things run a bit rich (due to the restrictions on flow they add to the situation). Report back on both tests.

Keep in mind that we don't have many "tune able" features on 97's . . . so as with all carbureted engines, we have to compromise between performance, power and fuel mileage. It is better to be a bit rich - than to be too lean.

[glennpm]

Originally Posted by Bored&Stroked

I'd follow the advice of Uncle Max. Where do you have your O2 sensors mounted and are you sure there are no upstream leaks - like with "slip on" extension pipes and u-clamps?

No slip-ons and I did tighten up my manifold bolts and header flange to pipe. The right rear was a little loose and tightening it did raise the AFR slightly.





You have to make sure that the system is 100% sealed - before your O2 mounting location.

Yes

Plugs: It is really hard to read plugs these days - the fuels burn so clean that it is rare to see chocolate coloring like in the "old days". Trust what the AFR gauge is telling you and make sure your timing is correct. Obviously, you don't want to be too lean or too advanced and cause detonation. I'd shoot for 24 degrees of total advance (around 2000 rpm or so).

Yes, I have 7° initial. I forget the total with my crab.

97s: I've found they tend to run a bit rich when under heavy load (power valves open). I would do a few road tests ---> partial/normal acceleration vs putting your foot into it. Mine tend to dip down into the high 11's or 12's under heavy load.

Shits and Giggles: You might also run your road tests both with and without those air-cleaners. You'll probably find they make things run a bit rich (due to the restrictions on flow they add to the situation). Report back on both tests.

Will do ...

Keep in mind that we don't have many "tune able" features on 97's . . . so as with all carbureted engines, we have to compromise between performance, power and fuel mileage. It is better to be a bit rich - than to be too lean.

Yup!

Thanks for your help B&S!

Glenn

[glennpm]

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Well consensus is to ditch my VW paper filters, Max said the same, and I thought they were an improvement over the chrome slotted helmets. I guess my filters don't suck enough though :-)

https://www.stromberg-bulletin.com/w...ir-Filter1.pdf

Weather is not great for the next few days so won't test without the filters first until I get the cloth re-usable ones that I just bought.

[Tim Ayers]

Originally Posted by glennpm

Well consensus is to ditch my VW paper filters, Max said the same, and I thought they were an improvement over the chrome slotted helmets. I guess my filters don't suck enough though :-)

https://www.stromberg-bulletin.com/w...ir-Filter1.pdf

Weather is not great for the next few days so won't test without the filters first until I get the cloth re-usable ones that I just bought.

Strombergs are very sensitive to air flow restriction. I'm really curious on what your readings will be without them. The best set up is some type of 1/2 slash stack or Frog Mouth scoop (turned facing backwards). These provide no filtering, so there is a trade off.

I'm also assuming that you still have the chokes in there if Max did the carbs. Taking the choke plates out really causes havoc with the air flow. The blade helps direct air flow into the carb.

Somewhere there is a chart floating out there that shows the restriction on a flow bench with various air cleaner set ups. Those paper ones were pretty much the worst in regards to restricting air.

[mfirth]

Even a single carb on a stock engine will run like crap with a paper element in a "Chrome Bonnet". I still use the original 1960 screen mesh element & it works fine.

[glennpm]

Yes, I was deluded to think that my paper VW bug type filters would be better than the chrome helmets and never researched them which is not my norm. Just looking at those, although attractive, sure looked restrictive.

Yesterday I bought a couple of K&N clones from Speedway and they should do the trick. Before getting them, I plan to check things out with no filters. Yesterday I also read a few posts on using the scoops but don't like the idea of running them with just a bug screen but want filtration.

[glennpm]

Regarding the choke plates, I have both installed and aware of the need for them too. Max did not do the rebuild. Bob at "97 Heaven" did them

97 Heaven
1730 Pomona Ave., No. 13 Costa Mesa, Ca., 92627

[glennpm]

Originally Posted by Tim Ayers

Somewhere there is a chart floating out there that shows the restriction on a flow bench with various air cleaner set ups. Those paper ones were pretty much the worst in regards to restricting air.

I'd like to see this if you or anyone else here has a link or copy. Perhaps it is this one found yesterday and linked above and here.

https://www.stromberg-bulletin.com/w...ir-Filter1.pdf

Thanks

[Tim Ayers]

Originally Posted by glennpm

I'd like to see this if you or anyone else here has a link or copy.

Thanks

I'll try to find it. Give me a few days.

[glennpm]

I did some testing today after finally getting a half decent day here.

Paper filters:



Video of my AEM AFR with these paper filters.

https://youtu.be/UMD2C_2eVdM

Video as above with NO filters

https://youtu.be/aWlGw81n_9s

... and with cloth impregnated K&N type filters

https://youtu.be/aWlGw81n_9s



The K&Ns look good and I'll be watching them to see how they look after running some more. After oiling, they run rich. I did put about 15-20 miles on them before taking the video.

I'm also thinking about getting at least another power valve down the road.

Glenn

[Tim Ayers]

https://www.jalopyjournal.com/forum/...rg-97.1276250/

I believe this is the HAMB thread I was referring to

[glennpm]

Thanks Tim

Glenn

[glennpm]

7/19/25 30 mile ride

Still running rich:
- Cruising AFRs are high 10s to the 12s or low 13s
- Giving it gas, APRs are in 10s
- Heavy throttle, 10.-10.3 or so
- Getting a little surging which I didn't have with paper filters

I also just sent a note to Charlie Schwendler

Glenn

[glennpm]

Got the carbs cleaned up and finished installing the smaller jets and PVs this afternoon. A ten mile test ride and it is excellent. Started on first crank too.

My AFR gauge jumps around and not sure why, but the the mean values are a definite improvement toward leaner and works great with full throttle. I just have the idle needles at 1-1/2 turns out and will tweak them a bit later and see how my gas mileage is now. Gone for the next week but glad to get this done before travel in the early morning.

This seems to be the way to go:

"From Uncle Max, re. dual 97s:
https://www.jalopyjournal.com/forum/...t-jets.419923/
"I don't believe in adjustable jets. (where's the baseline?)
I do believe in marrying the right jets with the right powervalves, remembering that a properly functioning powervalve starts to enrich the mixture at about 1/2 throttle - due to the "hydraulic" action of the accelerator pump, and becomes fully open at the end of the stroke. I also believe, for your flathead, assuming your're not planning to do much driving in the Andes or Himilayas, the best choice is .043 mains & number 69 powervalves. Set it and forget it.
No Strombergs were killed or injured during this post. . ." :-)"

[glennpm]

Regarding the AFR fluctuation, I'm going to vacuum adjust the idle screws add some MMO and drive it some more. I'm thinking it may be a sticky valve. I adjusted the valves not that long ago in mileage time that is. I'm off for a week now.

Glenn

[Bored&Stroked]

Great news Glenn . . . seems you're getting it dialed in!