Air/Fuel Ratio Meter

[RAC68]

Hi All,

Hi All,

I am playing with the idea of building a simple set of Air/Fuel meters based around 2 (1 per Carburetor) wide band heated O2 sensors. First, is an Air/Fuel meter a good way to adjust our carburetors? Second, although the web has a number of DIY choices for meters construction, I would like the group’s input on where and how to place the O2 sensors on a non-permanent basis.

Ray (64BJ8P1)

 

[57_BN4]

Ray,

Wideband gauge-type controllers aren't that dear, why would you want a DIY kit with all its attendant problems like latency and how to know it is calibrated accurately? Controlling a UEGO sensor isn't a trivial exercise.

A good wideband sensor and display will quickly show up carb weaknesses- they aren't very accurate and they aren't very repeatable when it comes to maintaining any particular Lambda or a/f ratio under normal driving conditions. Old engines don't need accurate fuelling so it doesn't really matter on a fairly standard engine. IMO, trying to set idle mixture with a wideband is an invitation to fiddle endlessly with the mixture nuts. An engine that holds an even idle note when warm is about as accurate as you are going to get.

For a modified engine a wideband display in the cockpit will do very well to set up full power fuelling and is far cheaper than a day at the rolling road.

Andy.

 

[drambuie]

I agree, You will be endlessly messing with the carb ajustment with all the outdoor temperture changes anyway. Why bother! Just enjoy the thing!

 

[RAC68]

Andy/Drambuie,

I appreciate your comments although I am a little disappointed. Since I have been fiddling with the SUs for years, I thought an air/fuel meter would reduce the frustration in carburetor tuning and provide a more accurate setting. I am not looking for a useless effort.

Thanks guys,
Ray (64BJ8P1)

 

[drambuie]

Hello Ray,
Personaly, I think part of the charm of owning a vintage british sport car is accepting them for what they are, And maintaining them as such. Using timing lights, feeler gauges, Checking spark plugs and dialing in the mixture evenly on both carbs to get that light brown color. Not to rich, not to lean. Adjust your idle and off you go! When the weather gets colder.... Expect your idle to go higher, When the weather gets warmer is settles back down again. My 1979 Electra Glide does the same exact thing with its S&S carb. Again, just the Nature of the vintage design. I get perfect tune all the time with my 350Z Roadster with all the high tech gizmos. When i open the garage door, I just choose, Old world charm, or high tech! To be very honest, 95% of the time i pull the cover off my 67 BJ8, slide behind the wheel, Pull out the choke,turn the key and smile as the smith gauges come to life. Maybe thats why my 2004 350Z has only 20k on the clock

 

[Bob_Spidell]

Well said.

 

[Frankenhealey]

Ray,

For a modified engine a wideband display in the cockpit will do very well to set up full power fuelling and is far cheaper than a day at the rolling road.

Andy.

They're great for setting WOT fuelling and comparing needles but for day-to-day driving setup probably too much information.

 

[RAC68]

Thanks for all the comments. I whole heartedly agree with the sentiments stated by Drambuie. Over the 48 years I have owned my Healey I have preserved the original feeling and try to drive it at least once ever couple of weeks. However, when it comes to setting the carburetors, I have never been sure of getting the settings quite right and thought an Air/Fuel meter could provide the proper indication.

I have always seemed to be running a little rich and usually get around 17 mpg. On a relatively recent thread, many indicated getting well into the 20 mpg range and my thought was…am I doing something wrong? Having mistakenly shaved 60 thousands (instead of 6 thousands) off the head back in 1971, I have been forced to use high test gas. I am planning on a few long trips with the Healey in the coming future and looked to better carburetor tuning to improve gas mileage with a related reduction in trip costs.

Thanks again,
Ray 64BJ8P1)

 

[big6]

RAC68
Are you running the original point distributor? Have you considered an ignition upgrade?

 

[John Turney]

.... However, when it comes to setting the carburetors, I have never been sure of getting the settings quite right and thought an Air/Fuel meter could provide the proper indication.

....

Thanks again,
Ray 64BJ8P1)

You might want to consider a (or a pair of) Colortunes. They will be less expensive than a Air/Fuel mixture meter setup and are more "classic-tech". The basis of the Colortune is that you install a clear spark plug and adjust the fuel/air mix until you get the right flame color in the combustion chamber. Kind of like adjusting a gas stove.

I have a pair of them, one for cyl #2 and one for cyl #5. After I get the right color in the cylinders, I put the regular plugs back and put a little green Locktite on the SU adjustment screws so they stay in place. Works great.

 

[PAUL161]

This is what I use and have no complaints. Unisyn flow meter. PJ

 

[57_BN4]

Actually, there is a slight difference between setting the idle mixtures and knowing the cruise/power mixtures are ok, particularly as you mention your engine is inadvertently modified by raising the compression ratio.

Since you are interested in more MPG then fitting a wideband to the tailpipe in a purpose-built holder is a very good start as you will have a direct reading of cruising a/f ratio which is predominantly controlled by needle profile rather than idle mixture setting. If your needle profile is giving too much fuel at cruise then no amount of tinkering with idle mixtures will change that.

I use this gauge and am very happy with its performance. It doesn't take much running with a rich mixture to burn up $200 of extra fuel these days. You can make an adapter to stick in the tailpipe so no modifications required to the car, or they do sell a somewhat overpriced one.

Andy.

 

[RAC68]

Hi all,

First, Big6, I am using a Crane CD ignition (Allison failure replaced by Crane) and have not experienced a miss to at least 5500 RPM. John, I have 2 Color Tunes and have found it very difficult to see a change in color (even in the dark) when adjusting the richness. Paul, I do use a Unisyn to balance the carburetors but that does nothing toward setting the richness of each.

Andy, if I understand you correctly, it may be worthwhile to use an Air/Fuel gauge to monitor changes in pin profiles with regard to richness at running speed and not to use the meter to set the idle mixture. Happily, there is no smoke emanating from the tail pipe at any speed and, although the carburetors have been rebuilt over the years, pins and seats are original.

How would I identify which pins are in the carburetors and what pins and seats to replace them with?

Boy, I like this forum as I am always learning something new about a car I’ve owned for 48 years. After all these years, the Healey is still alive.

Thanks all,
Ray 64BJ8P1

 

[Bob_Spidell]

If by 'pins' you mean 'needles'--think there's a song in there somewhere--just google 'SU needle chart' and you'll get tons of info.

Here's a couple:

https://www.teglerizer.com/suneedledb/index.html

https://www.sw-em.com/su_carbs.htm

The needle type should be marked with a fine etching on the base.

If by 'seats' you mean 'jets,' they come in a set size depending on the carb-type. The needles are tapered, and the diameter at fixed points--called 'stations'--determine the profile of the needle, which in turn determines the fuel flow available at a given throttle position/air flow.

The 'usual suspects' carry 'normal,' 'rich' and 'lean' needles (rich are skinnier than normal, lean are fatter). They're all the same diameter at the first station; that is, at idle. If you have a dyno, a lot of patience and a lathe you can turn down the needles at certain stations to get a more desirable mixture at that power setting. Not necessary for us average Joes.

Don't recall if you're the owner with the mileage problem, but if so I'd look at other things before worrying about the needles. If you're not blasting black smoke going down the road and the car runs fine probably something else is the problem. If you've got very high compression the mixture may be set rich--which applies across all 'stations'--to avoid pinging, which would certainly contribute to poor mileage. FWIW, I get about 23MPG at 65MPH average cruise speed, but it drops off quickly pulling a load or hotdogging. City mileage is 16MPG at best.

 

[57_BN4]

Andy, if I understand you correctly, it may be worthwhile to use an Air/Fuel gauge to monitor changes in pin profiles with regard to richness at running speed and not to use the meter to set the idle mixture.

Yup. Carbs assume the engine requires X amount of fuel for any given load based on the manufacturers pre-production development work. EFI OTOH compensates for a whole range of things hundreds of times per second based on a whole load of sensors on the engine which is why modern cars generally get better fuel mileage than old'uns. Carbs also have a built in safety factor too, for example the manufacturer will tend towards an overly rich mixture under full power to avoid any warranty claims for melted pistons should the conditions change from what they tested before production.

As determined fiddlers with modern tools we can be smarter than the manufacturer's judgement. By using a Lambda gauge we can measure the actual a/f ratio under driving conditions and adjust it to a more appropriate value by changing the needle profile. There are hundreds of needle profiles put out by SU for different applications and you can fiddle till your hearts content. When I was a lad doing dyno testing We'd have a leather belt with all the common needle profiles stuck through it and would run a car up, change needles, run again etc until power was optimised. Not very scientific compared to today's data logging capabilities but it sold dyno time.

Start with a pair of new jets- they aren't that dear. Then play the swapsies game with needles based on what readings you get and what information you can find online. If like me you are an obsessive fiddler, determine the carb piston lift under the conditions in question and start sandpapering the needles. Hours of fun.

Or just enjoy driving a piece of history that few get to enjoy.

Andy.
Who knows that the mother of invention is people that can't stop fiddling...

 

[JeffS]

I use an older Innovate Motorports (handheld) LM-1 meter with their portable tailpipe clamp for tuning. The last thing I want is a constantly changing meter in my own car all the time, drawing my eyes continuously away from the road.

Checking mixture accurately at idle and at cruise speed and at WOT is the only way to know if you have the correct needles installed in the carbs. For those of us who can't leave well enough alone, we get a better running car from our investment.

I like the tailpipe clamp, but know there's a bit of a reversion problem that shows a leaner mixture at idle. At slightly elevated speeds, the exhaust pressure overcomes that reversion. If you plan to mount a sensor (or multiple), keep in mind that high temps can really deteriorate the O2 sensor quickly if the mixture is set wrong, and most sensors actually recommend being within a certain temp range. It would last longest just behind the collector.

Those who say an O2 is a bad isea in a carbureted car are generally the folks who don't know how to use one and can't interpolate all the data. Generally they are the same people who think lightening a flywheel is a bad idea, or say raising compression means you have to run premium fuel.

And just a note on timing, tuning fuel mixture should be done after the valves are freshly set and the advacne curve in the distirbutor is confirmed to be correct for the engine so your timing is accurate at more than just idle. CD and electronic ignitions are just a replacement for points, not a replacement for accurate timing.

 

[John Turney]

Hi all,

.... John, I have 2 Color Tunes and have found it very difficult to see a change in color (even in the dark) when adjusting the richness. ...,
Ray 64BJ8P1

My guess is that if you can't see a change in color it's because your mixture is way off.

I have found that the transition between bright flashing yellow (rich) and faint dark blue (lean) happens within a quarter or half turn of the mixture screw. If the mixture isn't at that transition, the color change, either yellow or blue, will be slight with changes to the mixture screw.

 

[Trevor Jessie]

I installed a WB O2 sensor in my car just to see how the car performs with the carbs before I start engineering my FI system. I was some what amazed at how well the SU's mixture performed. It turns out (with my current needles) that I need to be set a bit rich at idle in order to have a proper mixture at cruise and WOT.

Before making tuning changes based on the sensor reading you need to understand what effects the readings. (As Jeff explains above)