Plans to Megasquirt my car got delayed over the winter so my Webers will stay on for another summer. So, I finally hooked up my wideband to see if any adjustments are needed to keep the engine happy and safe until I can do the conversion.

The only real "problem" area is idle and low speed driving on the progression circuit where it is running too rich. It idles smooth and steady at 700 rpm with AFR of 12.3. That with idle mix screws ~ 2 turns off their seats. That's the leanest I can adjust and keep the engine happy. Just off idle at 20-40 mph @3000 rpm it goes even more rich to around 11.0 +/- 0.5. I don't think that's alarmingly rich but wasteful and I do get a bit of annoying surging/bucking driving below 30 mph.

Current jetting is as follows:

Venturi - 28
Emulsion tubes - F11
Main jet - 115
Correction Jet - 200
Idle jet - 50

I'm thinking I should reduce the idle jet but not sure by how much. I can get .047, .045, or .040. Any suggestions?

I could also use some advice on mains and/or air correction jets. If I didn't plan to swap the carbs to FI, I'd try for a little leaner highway cruising mix for better economy and maybe flexibility. In limited testing running in good ranges for performance at the expense of economy - WOT ~12.5, Highway cruise ~13.5 but rarely goes above 14.0 even on downhill and decel. Weather is crappy here this weekend so I've only done a short drive in hilly conditions. I need to get it down in the valley for some long level runs to see where it settles. I think I can live with the numbers I'm seeing now, but do wonder what it will do when I attempt to cross a 10,000 ft. pass. I'd rather it not die of oxygen starvation if I attempt it. Any thoughts?

BTW, I live at 6,000 ft. elevation so I'm not surprised it is running on the rich side with out of the box jetting.

Warning: you’re measuring using an electron microscope and trying to adjust with a sledge hammer.

Chasing stoichiometric mixture of 14.7 (100% gas) is folly with carbs.

Stoichiometric is a moving target. It is about 14.0:1 for E10 since the ethanol brings along its own oxygenation. Do you know what is in your tank at any given time?

Also know that even with FI, there are plenty of times when fuel is being thrown at the engine to control temperature off the engine, address detonation, or to cool the catalytic converter.

Engines rarely make best power at Stoich. This chart may help.

Click to view attachment

Ultimately you need to feed more fuel to the leanest cylinder. But, I don’t think you’re monitoring AFR on a cylinder by cylinder basis so trying to get to 14.7:1 at the tailpipe could leave you very lean at one cylinder.

You are better off tuning by plugs, power, and cylinder head temps than chasing Stoich that may very well leave you running lean on high load grades, at elevation where you have less oxygen.

What I can tell you is that back in the day, carbs tended to be run rich both for power and to accommodate the need to drive coast to coast without putting holes in pistons.

https://www.youtube.com/watch?v=lG1OHoqeQTU


I think think you’ll be fine on carbs at 10,000 feet. Try to keep up with the Rambler

if you are at 2 turns, you are running on the lean side for your idle circuit and need a larger jet

What size is your engine? Have you adjusted/balanced/equalized the airflow of all six throttles at idle?

My car was adjusted at a much lower altitude then brought to 6000 ft. Here is what an old Porsche mechanic set mine to and it runs pretty well with Dual W40s at altitude.
I'll put them in your order for easier comparison, the book lists them differently.
Venturi 28mm
Emulsion F11
Main 1.15
Correction 2.10
Idle .55

Thanks all. The engine is stock 2L (1971cc) with european pistons getting 8.2 compression. The carbs are balanced for air flow (4 throats). The car is running great except the slight bucking at low speeds when running on the progression circuit.

@Superhawk996 I'm not chasing stoic at all. In fact, I'm completely ignoring stoic. AFR 12.5 at WOT and 13.5 accelerating or hill climbing seems good and I'm happy with that. What surprises me is that it doesn't lean out when the throttles close on decel or downhill. I would also expect a leaner mix at steady highway cruise although I need to collect more data on that. That makes me wonder if it is starving for air which is what I would expect at my elevation. Interesting that @NARP74 is running a larger correction jet than mine. That said, I'm happy with these numbers so long as the car doesn't choke climbing Beartooth Pass. I'm skeptical though. I remember the days of trying to drive from Denver to the Eisenhower tunnel in a car jetted for low altitude (not fun). And not being able to start a VW bus parked at 11,000 ft. at a remote trailhead after a week of backpacking. Call me paranoid

The real issue that I would like to address is the rich mix a low speed. @rfinegan , if I tune the idle mix by ear, I'm about 2-1/2 turns out on the screws which is right where Bob Tomlinsons' Weber Manual says is typical. However, the AFR at that setting is in the low 10s which seems way too rich for idle so I turned them back in a half turn where I still get smooth idle but a little more reasonable 12.3 AFR which is certainly not lean. Seems like a larger idle jet would be in the wrong direction. Also, there is the bucking I'm getting when driving at low speed on the idle/progression circuit. Tomlinsons says that is usually from too large of an idle jet so I'm a bit confused.

When the bucking happens does the AFR shoot to 20s? That would be leaning out. How does it feel if you pull the main stacks and just drive around on the idle jets?

Will have to wait for better weather before any more road testing. Pouring rain for the last 3 days and our gravel road is like driving through wet cement. However, I have six miles of data driving fairly level at low speed (20 mph) while the bucking was happening. AFR ranges from 10.8 to 12.3 with 90% of readings in the 11s.

Did not know you could drive without the main stacks in place. Will have to try that when the road dries out a bit

This morning I started from scratch readjusting the idle air mixture. Tuning by ear settles on the same 2 turns off seat as before. I readjusted the idle speed just a tad higher as I had it right on the margin before. Rebalanced the carbs. I'm now getting a steady idle AFR of 11.1 and the airflow reads just under 4 on the snail.
When I rev the car parked in neutral, AFR dips to low 10s as the accelerator is pressed and peaks at 15 when I let off before settling back to idle at 11.1. Again, I'd expect the AFR to peak somewhere closer to 17 when I come off idle.

BTW, someone will ask - the floats are adjusted properly.

Slight bucking at low speeds? How low and @ what RPM? What do your plugs look like? Drop down a gear or speed up and stay on the main circuit. It will hurt your MPG a bit but so what? That's the hand 100+ year old technology deals you.

It won't, and you shouldn't be too surprised. @bbrock

At decel (especially down grade) you have high vacuum below the throttle plate and you're pulling plenty of fuel via the idle circuit yet the throttle plates are fully closed and the only air is via cylinder equalization bypass and what little bleeds past the throttle plate edges.

No decel fuel shutoff like modern fuel injection.

As noted by Nditiz1 -- you can pull an awful lot of fuel via the idle circuit. Most people don't realize that they are running on the transition ports more often than the mains unless accelerating hard or under high load.

Don't know if you've ever stumbled across Performance Oriented website but wealth of information on carbs, jetting, etc. Primarily aimed at sixes but the Weber theory of operation is largely the same for IDF's.

http://www.performanceoriented.com/performance-tuning-2

I've said bucking but I think a slight surging is a better description. As long as I drive a steady 20-30 mph, you can feel the power hunt maybe a second or two between oscillations. I try not to lug the engine and keep it above 3000 rpm. Standard residential speed limit in our town is 25 mph and I'll go as low as 2500 rpm cruising those, but no lower. MPG is more important to me than HP. Fuel economy on this engine has been less than ideal, especially when I do much city driving. Of course, the ultimate solution will be to ditch the carbs. The more I use them, the more I hate them. I know some people love their carbs. I'm not one of those people.



Okay, that makes sense. It does bring me back to the idle jets though. Larger jets would let it suck more fuel (wasted) on decel - no? I assume most city driving is happening on idle and progression ports and that's where I'm running rich. I feel like a better number for those slow speeds running on idle jets and progression would be 13s or even low 14s since the load is light.

Yes, would agree under light load city driving, you're definitely on the transition ports.

I might be inclined to try a larger air correction jet.

Stealing directly from Performance Oriented w.r.t. air correction jet:

Larger orifice diameters shorten the duration and leans the fuel mixture delivered through the idle jet.

Looking at how NARP is calibrated at altitude, he's larger on fuel jet and larger on air correction. It very well be that both need to change to get what the engine wants.

But, if it were me I'd stay where you are on the idle jet and go larger on air correction trying to lean out the idle circuit a little and maybe move you to the main jet a little sooner. However, I think the problem you'll have is that if the air correction leans it out too much - you're going to end up backing out the idle needles more. The more you move them out the less effect they have as you get the needle taper further and further out of the needle bore orifice. You're already two turns out so I'm not sure you want to go much more. That may very well be why NARP ended up with a larger fuel jet AND a larger air correction jet.

Having said all that . . . you're not going to be happy until you have FI given your OCD nature ( ) and what you're trying to achieve (Fuel Economy). Per my 1st post, you're using a highly sensitive modern tool (Wideband AFR) to try to tweak an ancient technology (carbs) for Fuel Economy. You're bound to be left wanting what you can't have some where in the operating range.

@bbrock

Thanks. NARP said his carbs were tuned for lower elevation and then moved to 6000 ft. I assume he's happy with the tune though or wouldn't have posted.

I'll try larger correction jets for sure. CB Performance sells jets pretty cheap so I might go ahead and buy a set of .45 and .55 idles to play with.

You are dead on that I won't be happy until I get the FI on However, I'm not looking for perfection with these carbs, but would like to get a little better than low 20s mpg while I drive this summer and smooth out that low speed. Even though it is minor, that kind of drives me crazy. Performance-wise, the car runs like a champ. There is a bit to be gained in driveability though.

I'm off to collect more data.

They were originally tuned at a much lower altitude, ran like crap at 6k ft. I had them retuned at 6k ft and those are the numbers I posted. Not sure what they were when I got it here. It did run poorly before the retune, spitting and popping at idle and low cruise out of the neighborhood. Ran a little better after a warm up, but still not great.

Thanks for the clarification. Super helpful!

I have some better data now. I drove the car down to the valley (5,000 ft. elevation) where I could find long stretches of quiet road relatively level. It's clear the idle circuit is running rich. Consistently rich () through all speeds @~3000 rpm up to 50 mph.

0-50 mph: ~10.5 - 11.5 but mostly right at 11.0
Cruising level 50 mph: 11.5-12.1
Cruising level 60 mph: 12.5
Cruising level 70 mph: 13.5
Cruising level 80 mph: 13.5 - 14.0
WOT: ~12.5

Even at high cruising speeds the AFR dips down to low 11s/high 10s if the throttle is backed off to just barely past idle.

It seems AFR is pretty good whenever it's pulling from the mains, but as soon as the throttles close to idle/progression, it pulls too much fuel.

I just ordered 2.10 correction jets and a set each of .45 and .55 idle jets. That way I should have a combo that will work better than the current setup.

Another thing to look at is the accelerator pump. If they are coming in too soon that could account for the low end richness. 47.5 - 50 have usually been good for the idle jets on these 2 liter engines. Your mains look really good.

Thanks. I wondered about that. IIRC I have the pumps adjusted fairly conservatively but will check. It is running rich even when holding the throttle steady though so won't rule out the accelerator pumps as potentially contributing, but don't think they could be all of the problem. Will definitely revisit the adjustment though.

Will be watching to see how this turns out with new jets. The data and your logic seems sound.

Nothing new to add but I did some reading (yes, dangerous) about the air bypass screws that led to some philosophizing. I'm a curious guy and need to know how things work. I was curious whether the bypass screws could be used to lean out the idle mix (as opposed to the mixture screw which only adjusts the volume of the idle mix introduced at idle). The quick answer is No, but it took me into a controversy over the bypass screws. The CB (Tomlinsons) Weber manual suggests turning the bypass screws 1/2 turn out in pretune settings which is what I followed. Most people say the bypasses should be closed except as needed to balance the idle air flow of barrels within a carb. Some predict dire effects if they are opened except to balance a barrel. Well, maybe, but probably not.

Thinking through it, the idle adjustment screws simply open or close the butterflies to get a desired idle. Open a bypass screw will raise the idle without changing the position of the butterfly. So the effect of starting with bypass screws 1/2 turn open is that the desired idle will be set with the butterflies more closed than if the bypass screws are closed. In theory, opening the bypasses could drop the butterflies at idle farther below the progression ports than if they were closed. That could create hesitation on acceleration. I don't know if the opposite could be true where having bypasses closed could result in butterflies engaging progression ports at idle which would be bad.

I'm not noticing hesitation on acceleration, but will make sure the bypasses are closed to see if it changes idle AFR at all. Unlikely since if anything, having them open a little should ensure I'm not drawing mix through progression ports at idle.

This all led to a bit of an epiphany about the Tomlinsons manual that so many of us depend on to learn how to set up carbs. It was written prior to the days of O2 sensors. Tuning was by ear and by feel. Maybe occasionally a dyno was used but even then I'll bet tuning for max power was emphasized and economy was mostly an afterthought. As a result, recommendations in that book tend to create rich conditions that will make an engine run well, but not necessarily efficiently. We could probably use an updated manual that walks through tuning carbs with a wide band. Then again, I've come to the conclusion that other than for nostalgia or originality, going FI is the better, and ironically IMO, the less complicated path. Still, I'm glad I tried the Webers. It has been an interesting journey.

During bench setup, you really should have the throttle butterfly set such that there is only one hole (the lowest - idle hole) open. All the other progression holes arranged vertically should be either blocked by the closed butterfly or above the butterfly.

Part of the problem with opening the bypass as you propose is that you will end up weaking the "draw" signal on the idle circuit by lowering the vacuum below the butterfly when it is closed. Likewise it will also decrease the transition signal to some degree as the throttle begins to open.

Honestly, I have never tried what you've proposed. Give it a try. I suspect you're going to find some negative aspects to idle stability and/or transition as the throttle opens.

@bbrock

You need to get off your transition slots it they are open. This may be why your see a rich signal on the O2 on idle
No more than 1/2 turn from full close.
http://cbperformance.net/pdf/WeberIDFCarbs.pdf


Here is a tuning guide for Weber IDF and Wide band O2:
https://www.aircooled.net/how-to-use-a-wide...-flat-4-engine/

I think I'm going to disagree with this. What you say would be true if we weren't adjusting for a desired idle. The air bypass simply allows air to flow around the butterfly so it has the exact same effect as increasing the butterfly opening. If you screw in the idle speed adjustment to open the butterfly, idle speed increases. Likewise, if you open the air bypass screw, idle speed increases. Either is allowing more air to pass through the throat of the carb into the combustion chamber. So a change in one requires a compensating change in the other to maintain the same idle speed. I don't see how it weakens the draw since that would be determined by the total amount of air allowed through the throat (air going around butterfly + air through bypass). In other words, opening the air bypass is the equivalent of screwing in the idle speed screw except that the bypass only operates on one barrel where the speed screw adjusts both simultaneously.

Thanks for this! This gets really interesting though. In the aircooled.net article you linked written by John Connolly, He writes,



What's funny is that in this thread on another forum he wrote,


Later in that same thread he says he doesn't like the recommendations on jetting that CB gives.

So... It seems that Tomlinsons book is wrong, CB Performance is wrong, and according to John, John is wrong!

Obvious absurdity of contradicting information aside, those links you provided are going to be super helpful.

Thank you!

1)Opening the throttle plates will expose the transition circuit and add more fuel and air. Changing the mixture screw at this point will have little to no effect on the fuel being pulled from the transition slots.
2)Opening the air bleeds will allow a little air into the (1)carb(like the screw on our Djets) This can be used to balance a bbl that is not in sync with another, in sync to the others or as an idle control to a lesser amount.
3)Timing can be used to raise and lower the idle speed as needed too.

When you change you throttle plate location you need to reset your best lean mixture again on all 4 bbls

My earlier point about setting the bypass screws 1/2 open to start as Tomlinsons suggests is that it would reduce the butterfly opening needed to achieve the desired idle. In which case, less likely to expose the the progression ports. I can also see how it could cause the lag that John mentioned on that Shoptalk thread since I suppose you could end up with the butterflies so closed at idle there is a bit of lag between squeezing the accelerator and exposing the first transition port. I'm not saying I think Tomlinsons' procedure is the right or wrong way to do it, just stating what the effect is. I actually don't think my idle speed screw is anywhere close to a half turn out but will follow the aircooled.net procedure to make sure. That procedure makes the most sense to me because you wind up with throttle plates precisely where they should be.

I don't think you'll hurt anything by trying opening all the air bypass screws the same amount from the baseline balance setting. I've never really done it like that, but I know some guys who have used the air bypass to lean things out.

I'd get the balance correct and then open them all up an additional full turn, just to see what happens, you can always go back. With your O2 sensor and your ears you'll know if you get too lean.

I'm not sure I agree with this. The air bypass screw is not there to increase idle, but to balance flow. It is the same effect as drilling a hole in the butterfly, but not opening it. When you open the butterfly you expose more of the progression ports as rfinegan stated, which in turn is drawing more fuel and air into the throat.

Idle is the last thing you want to account for.
Balance
Best lean mix
Adjust idle
Maybe do best lean again
Finally adjust idle once more.

Each time you touch the idle screw you change the equation as to how much of the first progression port you expose. Which is why you will need to adjust the mixture screws again.

I'm not saying the bypass screws are there to increase idle. I'm just saying they DO increase idle if you don't compensate for the extra air by adjusting something else. If that something else is reducing the opening of the butterfly, it will move the throttle plate farther below the progression ports. Not saying it SHOULD be done that way.

Spent time over lunch and after work meticulously dialing in the carbs. I lost count of how many rounds of balance-lean idle mix-idle adjust I did. I am certain I am not idling with progression ports exposed. I checked with both a vacuum gauge and by ear on the advance vacuum port. For the idle mix, hooked up my low range tach instead of doing it by ear. This time the mix screws ended up less than 1 turn out from seated even after adding a half turn richer per John Connolley's method. Smooth and steady idle as before but the AFR still reads in the 10s at idle. I feel pretty confident a jet swap is in order. Can't say if it needs to go up or down but am betting on down.

I also pulled the main stacks and drove very briefly at lunch. I have two pro tips from that little misadventure.

1. If you decide to go driving around with the main jet stacks pulled, keep the stacks with you. They do you know good when you run out of oomph to get back up the hill if they are on the bench in your garage.

2. If you remove a CSP linkage rod to balance your carbs, it is a VERY good idea to put it back on before driving around with the main stacks removed. Running on 2 cylinders with no main jets will DEFINITELY not give enough oomph to make it back up the hill. Same as before, the rod does you no good sitting on the bench in the garage.

3. Bonus tip. If you ignore the first two, make sure you have comfortable footwear. You will need it.

Yes - I am a complete idiot. Luckily I didn't get too far away but did get caught by my neighbor who got a good laugh out of it.

Bigger idle jet, bigger correction jet.
If you want to properly measure each barrel to properly tune it (FI or carbs) you will need an exhaust port sensor (tangerine racing had these) to see what each cylinder needs for a mixture.
The merged exhaust is providing a merged A/F reading to any sensor which is an average.
Reading plugs helps, but really accurate sensors in each exhaust tube will be better.
Both fuel systems are a compromise until you tune it for each cylinder.

Another dumb question here but should I be setting my idle with vacuum retard plugged? With it connected, my engine wants to idle at 700 rpm rather than 800 which is fine by me (less fuel and quieter), but just curious if it that makes difference tuning the carbs. I think if I tune to an 800 rpm idle with the retard port plugged, I'll wind up with too low of an idle when the canister is plugged in.

I don't want to get into a debate over best dizzy or whether the retard should be connected or not. Those have been hashed out on other threads and I've made my decision after a lot of trial and error.

You will want to tune as though everything is in place, so distro vac in use. I believe the most ideal is with the air filters in place as well. They have a minor and probably almost non-existent impact.

Also not going to get into any debates with Dizzy's BUT SVDA style ones do have benefits to the smoothness of off idle. I'm guessing you have one since you are talking about the vac.

800 seems low to me. I usually tune carbs to 950-1000.

Thanks. Tuning with dizzy hooked up and air cleaner on makes the most sense to me, but I'm still wrapping my head around the idea that larger idle jets will lean the idle circuit so what do I know?

I'm actually running the stock DVDA dizzy with the trigger point opening blocked off. I tried a 050 but didn't like it. Bought an SVDA and it was good but I actually liked the response of the stock dizzy a little better and having vacuum retard for lower idle and emissions was the tie breaker. I've been very happy with it. Maybe that will change after I get the idle leaned out.

I'm not understanding how increasing idle jet will decrease fuel in the mixture. Does not compute...



I was looking back through my notes about the air correctors, but then remembered the
air correctors are in the main stack which would only affect the main circuit. You can actually remove the air corrector jet which will be the same as adding a 300 air corrector. This will bring in the mains sooner, but it is only a test to see if that will clear up the transition issue.

I did however stumble across this exact problem in a discussion with John ACN. I was getting 11s in the just off idle light throttle. I was running 50s at the time and dropped them down to 47.5 and it brought me into 12 to 13.

Jumping in late to this convo, but I’m going through similar analysis paralysis issues on my 6. Had a single wideband per PO in banks 1,2,3, when tuning by ear seemed ok, but felt I was missing something. Plugs on 4,5,6 told me I was running rich. I installed 2nd wideband on the 4,5,6 side and sure enough, tune was not balanced at all. Got it running better, then started to wonder about each hole…..

Bought this…

https://www.gunson.co.uk/product/G4074/Colo...e-Plug-Kit-14mm

Now I’m feeling much better about each cylinder…

Very interesting... It will be interesting to see how this plays out on my car. Right now I don't feel any transition issues but assume that might be because of all the surplus fuel swirling around at transition. It is easy to see when it switches from pig rich at 11 to 12-13s watching the AFR but it feels like it's pulling smooth and steady through the whole range.

The only way I could see larger idle jets would lean out the mix is if the extra fuel lets you screw in the mixture screws to be really stingy with the now even richer mix. I still haven't been able to grok how those work together. The ACN article does mention that a .50 jet can produce leaner idle than .80 but doesn't explain the mechanics.

The .45 and .55 idles should be here Saturday so am prepared to go either way. CB didn't offer a .475 so if I have to go smaller and the .45s are too small, I'll have to come back up a step (or is that a half step?).

I forgot about the color tune kits. Remember seeing someone post about them a year or so ago and thought they looked useful.

Since I'll ultimately be megasquirting this car, I'll call it good with the single wideband for carb tuning, but don't think I haven't fantasized about closed loop with individual sensors with the EFI

You can always open the .45 to .475 if they are too lean. Or if that works out to be what you need I think I have a set of .475...let me know (here) and I will dig them out for you...
Robert

Just ordered 2 of those colortune's last week. Hopefully they will be here soon. @infraredcalvin how was it tuning the banks with it?

Did you mention what your base timing is set at? And how much total advance @3200- 3500 rpm? This will effect your AF numbers too

Thanks! I'll keep you posted. I wondered about drilling but figure the bits would cost more than a set of jets. If I end up needing .475 and you have them, I can trade my unused jets for them.



I just set to stock specs of 27 deg BTDC@3500 rpm. I've never measured base advance since I just have a basic antique timing light. I probably should do that.

I have been following this to a certain degree as I am a carb guy and currently wrestling with a hex (hexed) bar linkage setup.

Couple things:

It's possible the technology of the Webers will never provide the information with regards to A/F numbers

Did you mention the car is running good? Maybe leave well enough alone until you can convert to an FI system

From what I know the idle speed screw needs to be about 3/4 turn max from initial contact. Also the mixture screws should be around 1 1/2" turns our from the seated position.

With the numbers you provided on the AFR were your cruising speeds under light throttle? I ask because you might actually be ok. If you are driving around 50 mph on flat ground you are most likely in your idle circuit still. It isn't until you open the butterfly more to drop the vacuum that you actually get into the main circuit.

Yep, light throttle. The transition seems to occur right around 50 mph on level ground as the AFR is pretty rock solid around 11.0 until 50mph/3200 rpm and then climbs to 12-13 territory. Even at 70 I'm under light throttle on the level but just above that magic 3200 rpm. Of course, level road is the exception rather than norm around here which is why my first set of measurements were all over the place what with accelerating, decelerating, and accelerator pump squirting every quarter mile.

I think the main circuit is in good shape, it's just the idle that is running rich. I also think the accelerator pumps were wasting a lot of fuel. I don't remember where I got the bench setting for them, but seemed adjusted way too aggressive. I have them disabled for now.

Depends on how we define "running good." If it means being able to drive like a bat out of hell and feel a strong pull all the way to 90, then it is dialed in to the nines. If we add fuel economy to the equation, it is not running good at all. The mileage sucks and I'm lucky to get 200 miles out of a tank of gas. I got closer to 400 miles when it ran on the long in the tooth DJet. I have a long trip I'd like to take it on the end of this month, but won't if I have to stop every 200 miles to fill it with liquid gold.

New jets are already paid for and on their way so should be able to do something to improve economy. Honestly, I never expected out of the box stock jetting to be ideal at 6,000 ft. so none of this surprises me.

BTW, the 3200 rpm transition squares with my brief time running with the main stacks pulled yesterday. As soon as I hit 3200, the engine leaned out and went dead until I brought the revs back down.

Totally worth the cost, the piece of mind is great. It’s a bit awkward the first time, but when you get them all dialed in you notice things are better balanced.

@nditiz1 There seems to be a pretty good range of “blue” light as you’re tuning, i set all mine just as it goes fat (orange) to blue, my wide band reads in the 11s, when I take it to the point just before it leans out (white), it reads 13/14s on the afr. Since I track my car, I’ve left it on the fat side for now.

I might have made some progress today. The new jets arrived this afternoon early enough to have a little time fiddling. I started by installing the .55 idle jets. At first I thought I was going to have to eat crow because when I started the car, it idled with AFR of around 12.8 which seemed like a very good sign. But after I had dialed in the idle mixture screws, the AFR was down in the low 10s. Wrong direction.

I swapped those jets for the .45s and went through a few rounds of balancing and adjusting the mixture. After adjustment, the car idles at around 12.3. I took it for a very short spin at low speeds and the AFR seems to run in mid-12s and 13s up to about 3000 rpm and then leans out pretty much the same as if the main stacks were pulled before.

I had to call it quits for the night after that but am hopeful I'm headed in the right direction and the larger air correction jets smooth the transition between idle and main circuits. I'm only guessing of course, but that's where I'll start tomorrow.