Technical Tuning carb with a wide band air fuel ratio gauge

I was planing on buying a wide band air fuel ratio gauge to help tune the carb on my Y block. From what I understand, I can weld in a "bung" into the header and install the sensor, run the wires inside the car and watch the gauge then make changes in jet size as needed. I was hoping that doing this would show if I was rich or lean at wide open throttle, then tackle acceleration, to zero in on acc pump discharge nozzle size. Has anyone done this? any tips or suggestions? Running a Holley carb.

 

Check out Zeitronix.com Others on here know much more than I on this subject, hopefully they can shed some light on the matter.

 

Here you go, my Speedhut, stand-alone wideband. My setup runs better then it ever has since adding the gauge, just plan on a lot of test drives and carb work. I am running dual Carter W-1s so tuning was double the work. The real trick is knowing which way to tune and what parts to purchase. I had to shop e-bay for metering rods, I think I tried 6 different rods per carb with float adjustments in between, like I said, a bunch of test drives. You will know in a few miles which way to start tuning, it's that fast. I am running on the lean side since the 250 isn't a race engine, so I tuned for mileage and efficiency. All the raw fuel smells are gone, the exhaust smells much better, and it starts right up. The good thing about the Carters is the three step metering rods, so I could tune for each step of the rods. Your Holley will be a little tougher to tune since they only use jets.



Speed hut makes it easy to install, with only power and ground wires, one light wire, one bung to weld in, and routing the cable into the car. They also offer lots of free options to make the gauge unique to your car, or they can match the OEM gauges for extra costs. I no long watch the vacuum or tach, but since tuning, the vacuum is much higher at road speeds.

 

Thats about the way they work,
They wont make you a tuner but give digital feed back for the changes you make,
Make notes and understand the carb is something you need to know

 

https://www.jalopyjournal.com/forum/threads/air-fuel-ratio-wideband-kit.1093910/#post-12406451
The above may help.
Pete

 

Couple things. Wide open throttle IS acceleration. What you want to focus on first is jetting. Now keep in mind racers will often change jet size depending on the density altitude at a given track, or because of other conditions, because it works. Also keep in mind though, they have one mode of operation - wide open throttle. So you kind of have to get it through your head that what drag racers do is not necessarily a good idea for those of us tooling around on the street. I think it's tough to over emphasize this. Whether it's camshaft or intake manifold selection, gearing, carburetor size, a lot of people seem to want to use components that are really only suitable for 5,000+ RPM, and then they want to try to drive around town. Another strategy you'll hear people use with a street driven car with a "bog", is Jetting up 3 or 4 sizes. It WILL get rid of a "hesitation" but that is not the correct way to go about it, because it will run pig rich on the highway.

Assuming you want to drive on the street, and at least casting a jaundiced eye at economy, and you don't want to keep the pedal to the floor ALL of the time, first use your wide band sensor to select the jet size at steady level cruise, in high gear, on the highway at say, 60 mph. (Make sure you're done $&cking around with float height, the ignition curve and the timing is right, and you've a good hot spark.)

You've also plumbed a vacuum gauge into the cabin so have been observing the manifold vacuum at idle, transition, and steady cruise, hills, etc. Nod your head yes....

The key there is that you don't ever want the power valve to open, except when it's called for, or it will run absolutely pig rich all the time. Also if you are jetted too rich it wastes gas, and can wash piston rings. If you know what the manifold vacuum is for your engine cruising at 60, a power valve can be selected that is very close to optimum. Every engine is slightly different, and local altitude plays a big role here. A 7.5" power valve might be stock though not in Leadville.

So now you're cruising along at 60 mph in high gear on level ground, know for a fact the power valve is not open. Jet up or down as required incrementally until your target AFR is reached. Keep in mind that at a steady level ground cruise, there is very little load on the engine, so lots of ignition advance will be utilized in order to light off the very lean fuel mixtures that result. Remember this strategy has absolutely nothing in common with pure performance applications.

The reason to do the cruise jetting first is because once you get the jetting where you want, it may well be too lean at WOT. Factory carbs run fairly rich (usually) out of the box. Timing curves conservative. Why? Because they don't want dumb shits to grenade their engines, warranty service etc.

Remember how drag racers jet up or down depending? Jet size has a direct impact on the WOT AFR, even though strictly speaking jets only technically really come into play at steady cruise above say 35 or 40 mph. You could actually remove the jets entirely and drive around the block at slow speeds. That leads to the next point. Each carburetor circuit is tuned independently, don't compensate adjustments in one to compensate for another. The idle circuit is important, because it runs into the transition area - where a lot of driving is done, but the AFR there isn't too critical. Leaner than stock, somewhere around stoichiometric 14.7 is good. Excessively rich idle AFR will foul plugs.

So jet it down at highway cruise till it squeeks. Then measure the WOT AFR. Usually around 12.5 AFR is considered safe. You will likely need to enlarge slightly the PVCRs with a pin vise. Just a couple thou. You never, ever, want to go lean under power, under acceleration. Think of an acetylene torch when you start feeding in O2.

Remember the power valve is all about (mostly) when the extra fuel comes in, not how much. If you take the time to really dial a carburetor in it pays off in terms of keeping the engine clean and being able to both light the tires off and get optimal mileage. The Y block in my truck went from around 9 mpg with a good tailwind to 16+ hwy.

 

I have set up my coupe the same way but I haven’t done any tuning yet. I put a bung in both side. I’ll be watching here.


Sent from my iPhone using The H.A.M.B. mobile app

 

What I noticed is even the littlest changes can effect the whole setup. I was having trouble getting the just off idle AFR leaner, it stayed around 12.5 till I got up to highway speeds. I lowered both floats in the W-1s about .030", this threw the whole setup way lean from idle to WOT. It took numerous tries to get it all back to where I was happy with it. Even a .002" smaller or larger metering rod will effect the AFR by a point or more. I made a very simple gauge out of cardboard with a pointer and pull spring. I tied the other end of the string to the throttle pedal and mounted the gauge to the dash. I wanted to see how much throttle travel I was using, turned out 90% of cruising around was at 15% to 20% throttle opening. The only time it was wide-open was playing around and normal highway driving never exceeded 25% opening. So think about how you really drive the car.

At some point you will have to decide when close enough is good enough. When you finally get it close, the weather will change and all the setting will off again, so be prepared for that.

 

I was told to put the bung about a metre, ( sorry- about 40” ) from the headers, in the exhaust pipe.
Would welcome comments on bung location, - does it matter?

A lot of great information on this thread.

Thanks.

 

Yes, a lot of good, no great help here! thanks. so I sounds like this is the way to do it, guess my first step is buying the gauge. I will order it today. Thanks again for the help.

 

Truck 64, Thanks for the detailed help, I'm sure that will help a lot.

 

Hey guys, I would like to jump in here, I too just installed an AEM AFR gauge but haven't even fired the engine off for the first time this season. I pulled the intake over the winter for some checking, minor mods, and to freshen up the paint.

I'm running lake style headers and due to the length of thr header I welded the bung as far out as I could, you can see the sensor by peeking in the end is the tube. My question is when I fire her up I'm going to need to balance the three Stromberg 48's reset my timing and idle speed and maybe hit the idle screws a bit. I also need to cure the fresh high temp paint I'm thinking I should wrap the sensor in the pipe with aluminum tape (yes-no?) or just plain foil to keep the sensor clean until I'm ready for it. I can't take the sensor out without unbolting the header. What your thoughts?

I'm starting to get a chubby just thinking about it.

 

I talked to a local guy that was running a AFR gauge about my sensor being installed only about 14-16" downstream from the last (back) tube. He said don't worry about it, it will help keep the sensor cleaner burning off any carbon build up. I don't have any other choice because the laker pipes are here to stay.

 

I bought an Innovate MTX-L kit for an OT car, the manual says (I guess it applies to other brands/kits) the following regarding the bung and sensor (Bosch):

• Weld the bung at least 24 inches downstream of the exhaust port outlet (after the collector), or 24 inches after the turbocharger if so equipped. The bung should be welded before the X or H pipe if so equipped.
  
  
• Using a clock as reference, mount the bung between the 9:00 o’clock and 3:00 o’clock position. Welding the bung in the lower section of the exhaust pipe can result in sensor damage caused by condensation making contact with the sensor’s internal heating element.
  
  
• Exhaust leaks, camshaft overlap, and open (shorty) exhausts will cause false lean readings at light engine loads. Typically, once the engine is under load and the exhaust gas volume increases, you will see accurate readings.
  
  
• Do not pre-warm the sensor before starting the engine, simply start the engine as normal. Allowing the sensor to pre-warm before starting the engine will increase the possibility of damaging the sensor from shock-cooling.

 

I called AEM tech service and asked them about my placement concerns and they said.

"The instructions are our recommened method of installation. You can mount the sensor anywhere or anyway you want to".

That was a big help.

 

i was concerned about this also, thanks for the input

 

I have seen them shoved up the tail pipe and still read OK. Mine is about 24" from the exhaust valve. Once you get it tuned up right, there should be no worries about carbon build up!

 

Agree with all the above posts. I will add, that for the street, a carb with adjustable part throttle really helps the cruise A/F ratio. Q-jet is a fantastic carb for the street and pretty responsive to adjustments. I believe the Edelbrock is similar. Our part throttle A/F is 15:1 fuel economy is 5 mpg better on the highway since tuning.

 

I've just put a fresh flathead back in my roadster with 2 97's. my exhaust is done so I can't put a bung in, but I have dumps about 18" after my headers. I could bolt on a short pipe with a bung to the dump plate. how long do you think the pipe would need to be after the bung to keep a good reading??

 

AFR Values & Characteristics in Four Stroke Engines
6.0 AFR - Rich Burn Limit (engine fully warm)
9.0 AFR - Black Smoke / Low Power
11.5 AFR - Best Rich Torque at Wide Open Throttle
12.2 AFR - Safe Best Power at Wide Open Throttle
13.3 AFR - Lean Best Torque
14.6 AFR - Stoichiometric AFR (Stoich)
15.5 AFR - Lean Cruise
16.5 AFR - Usual Best Economy
18.0 AFR - Carbureted Lean Burn Limit
22.0+ AFR - EEC / EFI Lean Burn Limit

Lean Conditions - Common Side Affects
Hotter Engine Temperatures
Detonation / Pinging
Hesitation in Throttle Response

Rich Conditions - Common Side Affects
Engine Flooding
Decel Pop / Backfiring
Lethargic Throttle Response
Excess Carbon Build-up (sooty pipes)
Fuel Smell from the Exhaust

Borrowed from:

http://www.afrplus.com/AFRplus-unit-functionality.asp?#AFR-values
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I found it was mind of tough to find actual "how to" information. Lots of stuff how to install. How to read the AFR. Not much on what I wanted to do though. Innovate used to have a website forum, that went away.

One thing that maybe isn't intuitive to keep in mind, if the ignition system isn't at 100% - say there is an intermittent - it will give a false lean reading, not rich as one might expect. The O2 sensors do just that - they read the amount of O2 present in the exhaust, nothing else. So if the fuel & air isn't getting burned, as in the case of misfire, it will read false lean.

They are fun to use, up to a point. It's like being hooked up to an EKG. This stuff is supposed to be fun. The old school way was to jet down till it bucked or "lean surge" on the highway and jet back up two sizes. Practically doubling range was kinda cool though, and avoiding crankcase oil dilution. Just remember you can lean it out on the highway - low load - without fear of burning anything, but if it goes lean under power it is going to roast something right away, probably a valve. You can't lean it out like a fuel injected engine, and if the ignition is weak you'll be able to tell right away. Lean mixtures are harder to ignite. Finally the O2 sensor is an average, and only an average, of four (4) cylinders in the case of dual exhaust. So you're only as good as the leanest cylinder. Not every jug will get the exact same charge. Each jet size flows about 2.5% difference. A well tuned carbureted engine should run 15.5 to 16 AFR on the highway no problem. While 14.7 or "stoich" is theoretically perfect leaner mixtures are used for best highway (low load) economy. Under load/power far richer fuel mixtures are required.

I'm not sure what happens if you already have a catalytic converter and run lean on the highway. Part of the "smog" strategies in the early 70s was (apparently) to detune the engine severely. Retarded timing, low compression, and waste fuel out the tailpipe. Notice NOX pollution (stuff that, when exposed to sunlight, makes the reddish-brown haze over cities) spikes when the AFR is optomized. So they dialed it back, and then burned the waste in a catalyst exhaust. So it may be, not sure, if you have a catalyst exhaust, it will go Chernobyl if you lean it too far out on the highway.

 

Truck64,
I appreciate your instructional comments because you are talking about street driving conditions, not just wide open throttle. Most articles on this subject are written for drag racers.

On the other hand I have a childhood friend who had been a drag racers of some success for 50+ years, who says he has never used an afr gauge.

Thanks,


Phil

 

Part throttle with high manifold vacuum is best tuned by driving and observing ....Just jet one step or so above lean surge
Although it may not apply to many engines here, an efficient combustion chamber with a fast burn will likely make best power at 12.8 air/fuel ratio...

 

Well put.

 

Very useful thread and I've picked up some good info on some stuff I was unsure about.

I've been running an AFR meter in 41 Chevy coupe (355hp 350sbc, th 350, 10 bolt, 750 Edelbrock) and have only changed the primaries to the leanest setting possible with the Edelbrock tune up kit. It seems to work fine and runs great for the last 2 years or so.

What I've have found though is that I seem to be monitoring the AFR all the time (beats watching the temp or pressure though!) and when it flashes lean (but there's no major load) it's momentarily worrying! I'm thinking it's time to remove it as it's possibly a case of too much information, but I'm not too sure about that.

To explain the occasional heart in mouth moments; running down a freeway at 50 - 60mph and there's a slight incline requiring a touch of throttle to maintain speed: this results in the gauge reading more than a bit lean but there's no real load and no sign of detonation, and a slight touch more gas and it fattens up instantly. I'm thinking I could do with a change in the spring to bring the enrichment in a little earlier, or maybe I'm just suffering from information overload - the car is running absolutely fine (as far as i can tell) and if I didn't have the AFR meter I'd be none the wiser! I'm convincing myself, aided by the AFR graph posted earlier, that lean in WOT or even heavy throttle is where you don't want to be, otherwise all is good.

The really annoying thing is the little hairclips on the linkages that magically disappear and seem to be unavailable to purchase separately, making changes to the carb something you really don't want to do!

Chris

 

Truck64 thanks again for the input.
Any thoughts on O2 sensor placement with lake pipes?

 

That is what I will end up doing, I just have open lake pipes so I will make a pipe to extend from the header and install the bung in that. I'm guessing the bung will be about 18" from the last primary tube and be about 20" from the end of that temporary pipe. This complete set up will just be a temporary thing with the gauge just sitting on the seat.

 

Sounds like you could do that but if it does not stumble at that point, just leave well enough alone.

 

Happydaze
Have you tried to measure your highway mpg? I'm interested in tuning for better economy using ideas from this site.
Thanks.



Phil

 

Hey, Truck 64, that is GREAT information! !!!

 

I have, well kinda! I intended having a go at trying a variety of things but the loss of those pesky hairpin clips has set me back on that! When I eventually get some I'll most likely get back on it. But i did measure consumption on a decent run and if i recall correctly I felt it was pretty decent, well into the 20 something mpg's. This was a huge improvement from my staring point. Quick back story. Bought the car. Didn't run too well. Smelled very, very rich and would strangle itself from time to time. I had an AFR meter on the shelf for another project and decided to fit it for giggles. I found the anticipated very rich condition. Being in the UK I can't just go to the local speed shop to source a replacement. Went on a trip out (to a hotrod drag race event) and i guess the Holley carb took a total shit. Transpires it was a weird one that doesn't have the external float adjusters. Limped the last few miles to the event and was then 200 miles from home. Purchased only available for sale carb I could find, 750 Edelbrock, and I fitted it and was running straight out of the box. On the way home it was running pretty well and i left it at that for a few months. I then decided to maybe look for more mileage and did a jet and rod change which i guess improved mileage but don't know to what extent. And that's where I am now and haven't touched (or really used the car) for 6 months or so. Hunting for hairpins!
Chris