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Misc: Everything Else Air Fuel Gauge 02 Sensor Lambda Sensor


Glenliman

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I haven't read thru this entire thread yet, but I did see mention of John McDougall's bike with its O2 sensors up close to the exhaust ports.
Those are narrow band sensors which rely on exhaust heat. They have no heating element of their own so must be up fairly close to the action.
When fabricating the pipes for my 1360 I included an O2 bung for a wide band sensor just after the 2 into 1 collector. John's info was that with all of the O2 related tuning he never found the need to use different jets on one cylinder vs the other.
So the single hidden bung should do the trick.
Now an admission.
Ive never gotten around to checking the AFR and I'm not sure that l will.
The jetting was as suggested by Terry Prince for that motor fitted with Dellorto 41 pumper carbs. It seems spot on, which is interesting because Terry also mentioned that at that time no one had assembled an engine at that spec.
I think he based the info on Vincent 1200s with the same Manx style combustion chambres which he or his customers had built and fitted with Dellortos.
Making the engine bigger actually meant reducing the mainjets a little from a 1200cc engine size, which I did.This makes sense if you wade through Bernoulli's work.
Somewhere in there he explains that the flow in a Venturi increases at the square of the flow thru the main body.


I thought that if anything the engine might still be a tad rich, however on an easy cruise it managed 60 mpg Imperial, just a shade better than my standard 998 Rapide.
That was a pleasant surprise. I had made an assumption that with the large displacement high performance carbeuretted engine, fuel mileage might not be great, maybe something similar to to Buick Wildcat numbers.

It's feels good to go Green!

Glen
 
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BigEd

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Don't shoot me, as this post is not about the topic! This a great post by Glen. Honest, informative, a bit technical but not too technical for the average punter and nice humorous comment at the end. Thank you Glen.:)
 

Magnetoman

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Warning: Vincents use Amals, and this post deals with jetting an Amal aided by an air/fuel meter, but other than that it has nothing whatever to do with Vincents

I've been tied up with other projects the last couple of weeks but yesterday returned to jetting. The background is I'm trying to determine the minimum modifications needed to make a 2-stroke 1000-Series Amal Concentric work with a 500 cc Gold Star.

Yesterday I only had time to make a quick jetting run from which I determined the AFR was 10:1 at full throttle with its 290 main jet. From that I calculated to decrease it to get to 12:1 would require dropping the main jet to 10/12 x 290 = 241.7. Or, that using a 240 would give 290/240 x 10 = 12.08:1. However, after looking at today's results, which I'll discuss momentarily, I looked again at yesterday's, shown in the first graph. The fat green line shows where an AFR of 9.4 would be. Note that I was at full throttle yesterday for only ~2 sec. so it's possible the thin green line would have reached 9.4 in another second. Make a mental note of that.

OK, turning to today's results, and remembering that maximum engine power should be achieved when the AFR is in the range ~12-13, the second graph shows that with it held at ~1/8 throttle the AFR was 12.3:1. So far, so good.

The third graph shows that at ~1/3 throttle, where basically every variable in the carburetor is contributing, the AFR drops a bit to 12.0:1. Still, so far, so good. However, the graph also shows that at full throttle it drops to 11.0:1 despite my above calculation that it should have been 12.08:1. I'll return to this in a moment making use of the mental note you made two paragraphs ago.

The fourth graph shows that the second full-throttle run today resulted in a slightly higher 11.4:1 than the first run. However, note that it took 2-3 seconds for the ratio to drop to that value.

I used 10:1 from yesterday's run to calculate that I should use a 240 main jet today. Referring back to the first graph, if instead I had been able to hold full throttle for 2 sec. longer, and if the AFR had dropped to 9.4 in that time, then today with the 240 main jet the AFR should have been 11.36:1 at full throttle, which it was. That is, within experimental error the calculation I did yesterday to arrive at 240 gave the "correct" answer. However the "experiment" I did upon which I based the calculation wasn't run for long enough to achieve the steady state AFR value. The important point from this is that not only does the air/fuel meter tell you the AFR with the current configuration of the carburetor, if you run the tests for more than ~2 seconds it quantitatively tells you what changes to make to achieve the desired final result.

In light of today's longer full throttle runs, and using 11.0-11.4:1 as the values they gave, changing to a 220 for the next run should give 12.0-12.4:1. The smaller main jet also will increase the AFR somewhat at partial throttle resulting in values at all throttle settings falling in the sweet spot of 12-13:1 that gives maximum power.

As an aside, the jetting I used yesterday and today felt perfect at all throttle settings and rapid changes in throttle positions. At least, to within my ability to run full throttle tests on a Gold Star in an urban setting. Without the Innovate A/F meter I would have been happy with yesterday's 290 main jet, or with today's 240, even though it looks like 220 will be the one to use. Also, all of these settings are rich compared with stoichiometric 14.7:1. If I were tuning for economy rather than performance I'm not sure I could achieve it across the range with the present 2-stroke spray tube and air compensating passage that are part of all 1000-Series Concentrics (although, both can be changed). Certainly not with a .106 needle jet.
Innovate24May2019_01.jpg Innovate25May2019_01.jpg Innovate24May2019_01.jpg Innovate24May2019_01.jpg
 

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Cyborg

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Thanks again for posting that. It will (or should) help with my quest to jet the Comet’s flat slide. Unfortunately, I will also be tied up with other projects for a while.
1289F5EF-BCBD-4099-8D93-C3DD22E5E987.jpeg
 

Magnetoman

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Again, Vincent content of this post is tangential. My goal was to see if a 1036 Concentric could be made to work well on a Gold Star without changing the spray tube or drilling the compensating air passage. That is, I wanted to determine if it could be made functional with only the simplest swapping of a few screw-in components in one of these 2-stroke bodies.

I made A/F measurements under two sets of conditions, "static" and "transient." I made the former by holding the throttle in a fixed position for ~5 sec. before changing the throttle to a different position. For less than ~1/3 throttle these were made on relatively level ground as well as when going uphill and downhill. Higher throttle settings only were made going uphill to keep the speed within reason given the conditions.

"Transient" measurements were made by snapping the throttle open. I use a 1.55 V battery in my throttle position sensor so the first graph shows a 15-sec. section of the data where I was in 2nd gear at ~1/3 throttle (the red curve), then snapped the throttle closed and back open, shifting successively into 3rd and 4th where I finally gave it full throttle. The magenta A/F curve shows brief lean pulses occurred roughly 1/2-sec. after each of these throttle movements, but none are excessive and I felt no hesitation from the engine. In fact, I couldn't be happier with how the engine felt throughout this entire run.

As can be seen from the first graph, even in regions where I kept the throttle constant the A/F curves fluctuate by ~+/-0.5 around a mean value. Added to this is the mean value at a given throttle setting at different times during the run (i.e. possibly under different conditions of, say, uphill one time and downhill another) could vary by nearly that much as well.

Data from two runs, with nominal '220' and '200' main jets, are plotted on the second graph. Although I watch the bar graph display of A/F ratio as I ride, it takes the better part of 2 hours after each run to find on the stored data the one or two-dozen time intervals worth examination, copy them to Photoshop, format, print, and then mark the AFRs and measure the corresponding relative throttle openings from the 0-1.55V signal from the throttle position sensor. I don't think I could have guessed what this curve would have looked like from just having observed the real-time bar graph display.

The first thing to note is changing from a '220' to a '200' should have leaned the previous ~12:3:1 at full throttle to 13.5:1. Instead, the mixture became richer by the equivalent of having changed a 220 to a 225 rather than a 200. I've mentioned several times over the years that I measured a number of '500' Amal main jets on my flow bench and found 25% of them to be as much as 3½ sizes too large or too small. The other 75% weren't perfect, having a spread of almost +/-1 jet size. Anyway, as these two jetting runs show, the '200' in it now is somewhat richer than the '220' that was in the first run.

I don't know if the '220' is smaller than its marked size, or the '200' is larger, but they're close enough that it makes sense to plot both sets of data on the same graph. Unfortunately, to measure the relative flow of the two jets would require me to dismantle the carburetor fixture currently on my flow bench, which I'm not inclined to do because I have more measurements I want to make. After plotting all the data I examined the outliers to see if I had made any mistakes, or if I had extracted any of them from graphs where I hadn't allowed the mixture to stabilize for ~4 sec. This eliminated three potential data points, but the three x's between 0.4 and 0.5 are real.

The scatter of the data points isn't due to experimental uncertainty in reading the values from the graphs, it is real. The same throttle setting under different conditions (e.g. accelerating on level road vs. climbing a hill) gives somewhat different AFR readings. Also, after the first run the AFR at idle was 12.2, but after the second it was 11.5 even though I hadn't touched the mixture screw in the meantime, and even though the idle "felt" the same.

For throttle settings between 0.2 and 0.5 the mixture is slightly leaner than the "optimum" 12-13 for maximum power. Raising the needle another notch isn't an option because that would make it much too rich in that region. However, there are two reasons I don't think this region is an issue. First, the 12-13 "rule" is just a guideline, and only time spent on a dyno would determine if more h.p. could be extracted with slightly different mixtures. Second, most time riding is spent cruising at mid-throttle so having a slightly leaner, but still rich, mixture will save a bit of fuel without costing any actual performance.

Trying to find reliable information on the "perfect" air/fuel ratio for gasoline, let alone E10 or E15, quickly takes one down a rabbit hole. If information is correct that 13.5:1 is the ideal ratio for maximum power then the present ~12:1 robs me of ~2% at full throttle. However, if 12.5:1 is the correct ratio, my current jetting essentially robs me of nothing other than the price of having to refuel 4% more frequently if I ride all the time at more than half throttle. On the other hand, if much of my time will be spent between 1/8 and 1/4 throttle the current jetting will provide better economy at the cost of only ~1% of the power in that range.

The performance with both the '220' and the '200' main jets felt perfect from idle to full throttle, as well as when snapping the throttle open from various initial positions. So, this work shows it is possible to configure a "2-stroke" Concentric to work well on a 4-stroke machine. Like, say, a CometAFR_8June19_01.jpgAFR_9June19_04.jpg...
 

Cyborg

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Interesting.... the random relationship between the jet “size” and actual flow rate makes me wonder even more about the aftermarket jets that I purchased for the Mikuni. Have you ever had any Mikuni jets on your flow bench? Given the fact that there won’t be a flow bench in my future, I wonder if one could make a simple setup to check flow.

The .7 change in AFR at idle..... although not enough to feel any difference it still makes me wonder what caused it. Worn slide....global warming...as in all the good stuff vacated your gas tank in the Arizona heat?? It’s an Amal?
 

Magnetoman

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Have you ever had any Mikuni jets on your flow bench? Given the fact that there won’t be a flow bench in my future, I wonder if one could make a simple setup to check flow.
No, I've never measured a Mikuni jet, and there's no simple way to check flow so you just have to cross your fingers and hope the jets you bought flow what is marked on them. I've thought of flow testing all of my Amal jets so I can sort them in to compartments by actual flow rather than by stamped number. But, that's unlikely ever to happen.

As a digression, a high-born Indian colleague (son in the line of the only Indian ever raised to hereditary British peerage) told me a story of his time spent receiving his Ph.D. from Cambridge. His possibly apocryphal (or possibly autobiographical) story was that a high-born Indian joined a research group at Cambridge and, in what is a pretty common practice, was given an initial menial job to begin familiarizing him with the lab. He was to sort loose resistors back into appropriate drawers, but when the professor returned later in the day he saw the resistors still strewn across the table. When the professor asked why he hadn't sorted them the student replied "the boy never showed up." I'm waiting for the boy to show up so I can supervise him doing the work to sort my jets.

The .7 change in AFR at idle..... makes me wonder what caused it.
I actually don't think that is significant. The carburetor has less than 500 total miles on it (so the Amal is less than 50% worn out...). The fact the mixture initially goes rich as soon as the throttle is cracked open means something like only a slight difference in tension on the throttle cable would account for the different idle readings.

However, what is significant is I installed a different main jet that should have been significantly leaner but instead was slightly richer. That's why it would be nice if the boy would show up to sort my jets so when I want a jet with greater/lesser flow I would know that the new jet actually flows more/less than the one it is to replace.
 

Magnetoman

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I just finished modifying and jetting two Amal Concentrics for a Gold Star, requiring approximately 15 thirty-minute jetting runs totaling over 7 hours, covering ~200 miles, and resulting in ~160 pages of printouts of AFR data from my Innovate LM-1. At the risk of repeating a few things I've written before, some observations from this experience, in no particular order, are:

-- the bike "felt" like it ran fine for AFRs anywhere in the range ~10-15:1 so anyone who can correctly jet a carburetor by feel alone is a far better man than I.

-- watching the road while also mentally averaging the fluctuating AFR display and noting the throttle position would be hard enough, but to memorize just these two values for the at-least dozen throttle positions required to determine the full range of jetting is beyond my capabilities. Luckily, the Innovate LM-1 recorded the AFR, throttle position and rpm, freeing me to concentrate on potholes and possible sheriff's cars.

-- AFRs vary significantly depending on the conditions, e.g. accelerating up a hill, traveling on a level road, etc. This means that I actually needed more than a dozen readings to reliably determine the overall average shape of the AFR vs. throttle position curve for each configuration (hence the 160 pages of printouts).

-- because the AFR depends on conditions I will be adding an accelerometer to the "instrumentation package" in the future to make it easier to distinguish between AFR readings taken when accelerating, constant speed, or decelerating. In principle the rpm readings would be sufficient for this, but when analyzing 160 pages of data anything that makes the task easier is welcome. On this note, I can't imagine having done this without my Gerber Variable Scale and TI59 programmable calculator (vintage 1977) since I needed to normalize readings on the printouts from the throttle position sensor to the 1.56 V at full throttle.

-- it took a minimum of 15 sec. at full throttle while heading up a hill before the AFR stabilized at its final value. Attached is an example. I was going over 75 mph at the end of those runs which means during that time I covered ~1/4 mile. A shorter run reaching a lower speed would have given an erroneously high AFR reading.

-- at lower throttle settings the speed stabilized reasonably fast but I couldn't count on the AFR to stabilize until ~5 sec. had passed after I had reached that constant speed. Sometimes the AFR stabilized more quickly than this, but my default time at each throttle position was at least 5 sec.

-- a decade ago I measured a dozen new and used Amal jets of the same size on my flow bench and found 75% of them to be within +/-1 size of being correct. Unfortunately, the other 25% flowed too much or too little by as much as 3½ sizes. At one point when determining the jetting for the 1036 Concentrics I installed a jet marked two sizes leaner than the one that had been in it but the air/fuel gauge showed the nominally-smaller jet actually flowed a half-size richer. This was not the only time I ran into jet marking issues during this work. Keep this in mind if your jetting becomes too rich or too lean when changing to a jet whose marking makes it seem it "should" be correct.

-- wear or mis-manufacture of a needle jet by only 0.0005" is enough to completely wear out the jet (or make it too lean, if manufactured slightly too small). The needle jet in my Catalina Gold Star experienced that much wear during a 1200-mile ride so the needle jet definitely is not a set-and-forget component. As an aside, although the needle jet I used for my recent efforts is stamped 106' I previously had measured a large number of NOS jets using two different calibrated bore micrometers and found them to be 0.1065". This is how they were originally listed by Amal.
FullThrottle_240Main.jpg
 

Magnetoman

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Cyborg said:
I'm feeling quite smug now that I've one upped a experimental physicist.
I would rather stab myself in the eye with a fork than attempt to analyze 44 minutes of data.
Tormented for over a month by knowing Cyborg had a newer model AFR sensor than me, I had no choice but to address that unacceptable situation. So, in the spirit of nothing exceeds like excess, I upgraded my perfectly fine AFR system to the next level. In addition to having the latest Bosch wide-band sensor, I'm now instrumented to log, for up to 566 hours (vs. 44 minutes) continuously if so inclined, the AFR, throttle position, rpm, acceleration, and exhaust gas temperature. I have one unused position on the data logger so could add road speed with another sensor, but that would be excessive. Or, would it? Hmm... Oh, and I have a separate, Canadian-made, aftermarket knock sensor controller I'll be testing to see if it provides useful information. It turns out the head-steady lug on a Gold Star couldn't be a more perfect location for mounting the sensor even had it been specifically designed for that purpose.

This weekend I installed the new "instrumentation package" on my Gold Star Catalina, whose Monobloc I already had jetted to be perfect using the old school method of "feel." However, in addition to testing the new instrumentation, this week should see the jetting get even perfecter.

Unfortunately, no instrumentation upgrade comes without collateral damage. Now I'll have to spend time learning how to export the 566-hours of data to Excel as well as write a program to plot AFR vs. throttle position rather than slowly extract this information manually. I already know from my previous measurements that the AFR at a given throttle position depends on whether the bike is accelerating under load, at a steady speed, or decelerating on a downhill stretch, so I'll want my Excel program to incorporate data from the accelerometer. A scatter plot of AFR vs. throttle position is exactly what is needed to understand the jetting over the full range of operation. See what you've forced me to do, Cyborg!

The weather looks like it will cooperate for a few jetting runs this week by dropping to the low 100s. Unless something gets in the way I should be able to make my first runs on Wednesday when the high will be only 101 oF.
 

Cyborg

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I'm sure 566 hrs worth is good for a free one way ticket to the laughing academy. Interesting idea using a knock sensor, although I wonder if it can distinguish an actual knock from all of the other thrashing and vibrating going on.... I have no idea, but riding atop a liquid cooled modern multi cylinder would be a much more civilized ride for the sensor. It will be interesting to see how well it works...certainly worth a go. If you purchase a sub harness for the sensor, save yourself some heartache and make sure to get the new improved version that is rat resistant. It will likely have little drawings of rodents on the sheathing or a rat with a line drawn through it.


When they designed the Honda CX500 Turbo, rather than use knock sensors, they were able to program the ECU to avoid those conditions. Always thought that was a better way to go, because the knock sensor is telling you that things have already started to go to hell in a handbag.

I'm trailing far behind you.... but I did TIG weld the bung in place.

Does a bunsen valve's change to reversion in turn cause a chance to A/F ratio.... as in once the valve is removed, does the engine run richer?
#Shroderingerscat
 

Magnetoman

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I'm sure 566 hrs worth is good for a free one way ticket to the laughing academy.
If I survive getting the Excel program to work without it sending me there, dealing with the data only will take a few clicks of the mouse (says he, having had more than enough experience with such things to know better...). My hope is I'll be able to automatically generate a scatter plot, with the density of data points graphically showing what the AFR actually looks like as a function of throttle position.

Cyborg said:
BTW.... what are you using for an accelerometer?
Part of my new setup is an Innovate LMA-3 which includes two internal accelerometers.

Interesting idea using a knock sensor, although I wonder if it can distinguish an actual knock from all of the other thrashing and vibrating going on....
If it were made by an American or Brit I'd be skeptical, but it's made by a Canadian, and he claims it can do it, so it must be true...

Two things prompted my interest. The first was when I got my Catalina running a few years ago and I turned off a fast road onto a small, uphill street going too slow in a gear that was too high, the engine started rattling. I quickly grabbed the magneto advance lever and the rattling stopped. The second is my Competition has a 10:1 piston and needs high octane no matter what. I use a super-expensive octane booster that converts pump fuel into 100 octane ((R+M)/2) at a total cost of ~$8/gallon. Anyway, I wondered if a knock sensor might save me money if using it let me determine that less of the octane booster was sufficient (the savings in fuel cost could pay for the knock sensor system in less than 100,000 miles... but, that's not the point).

As opposed to the dull thud of an engine, or the rattle of parts falling off, "pinging" has a quite sharp sound so there is reason to believe an appropriate notch filter could isolate the desired undesirable signal from the normal sounds. The control unit has an adjustment to set the cutoff, and my hope is the unit will be sensitive enough to detect knocking before I do, either by hearing it despite the sound-deadening of my helmet, or the more obvious clue that the engine abruptly stopped turning.

Does a bunsen valve's change to reversion in turn cause a chance to A/F ratio.... as in once the valve is removed, does the engine run richer?
Interesting question. A bunsen valve represents a very low restriction to the outgoing exhaust, but there could be some effect on the strength of the reflected pulse since the pipe no longer would have an abrupt exit to the outside world. If its presence weakens that pulse, and if there is a lot of valve overlap, it would have an effect on the filling of the cylinder.
 

Cyborg

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Well if you ask me, you are treading down a road laced with land mines. What happens if the undesirable signal drives you to the point where you seriously have to consider programable electronic ignition with a VOS to switch maps? Going to be a tough pill to swallow for a magneto man.

As for the Bunsen valve, I figure if it is able to keep interloping O2 molecules away from the A/F sensor, then it “must” be having an effect on reversion which in turn has an effect on mixture.... especially with cams like the Gold Star’s or Mk2’s. If that video (post77) about the bolts and thumbscrews is to be believed, then the presence of Innovate sniffer itself would cause a change. The question is how to determine that. Now we can’t just let that question fester..... but how do you answer it?
 

Magnetoman

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What happens if the undesirable signal drives you to the point where you seriously have to consider programable electronic ignition with a VOS to switch maps?
There's no danger of that happening. My self-imposed (or self-inflicted) approach to old motorcycles is to keep them as original as possible, within reason. The "within reason" gives me the wiggle room to put a Concentric on a Gold Star, but not a Mikuni. I also enjoy (mis)applying modern technology to old motorcycles, but to make them work up to the full potential of their original designs and components, not to "upgrade" them. My approach gives me the flexibility not to paint myself into originality corners, but ensures I get the full "old bike experience" when riding those machines. Other bikes given me EFI, electric start, disk brakes, etc. when I want a different experience.

As for the Bunsen valve, ... The question is how to determine that. Now we can’t just let that question fester..... but how do you answer it?
It actually would be quite straightforward to answer. Someone with a modified pipe like mine, where the sensor barely protrudes, checks the AFR at all throttle settings, then slips a Bunsen valve over the end of the pipe, and checks again.

The wording with "someone" and "like mine" wasn't accidental. It's easy to get lured down some else's rabbit hole when you still have plenty to do down your own.
 

Cyborg

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But..... If installing the bunsen valve changes the A/F reading and presumably it will or we wouldn't have a bunsen valve to start with, all we would see is the change. Is the change only due to the valve preventing O2 from getting back up the pipe and altering the reading... or is it because the reversion is reduced and the intake charge is altered.... or is it a sum of the two? Is the baseline (obtained without the bunsen valve) accurate or has it been altered by those interloping O2 molecules. Again.. presumably it has. At the end of the day, you will have a motorcycle that runs and feels like all is well, but that of course is not the point. Cling to the rim of that rabbit hole all you want, but eventually all those years of academia will weigh you down and your compulsion for the truth will get the best of you.
 

Magnetoman

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Is the baseline (obtained without the bunsen valve) accurate or has it been altered by those interloping O2 molecules. Again.. presumably it has.
Not so fast with the assumptions. The environment for an O2 molecule in the exhaust pipe is like that in a Tokyo subway car at 5pm. The last person who manages to force his way through the door doesn't proceed on to the back of the car, but the pressure due to his presence does make it to the back of the car. Similarly, an O2 molecule sucked back up the exhaust pipe doesn't make it all the way to the exhaust port, but the pressure does. As long as a minimally-intrusive oxygen sensor is placed far enough up the pipe that oxygen doesn't make it that far then its reading will not be affected by the fresh O2 molecules that are further downstream.
eventually all those years of academia will weigh you down and your compulsion for the truth will get the best of you.
In times like these I take refuge in the words of Voltaire: 'Toute phrase qui a besoin d'explication, ne pas mèrite pas qu'on l'explique' ('Not everything that needs explanation, merits explanation'). Also, an invaluable piece of advice I was given years ago, after I had accepted my university position but before I had taken it up, is relevant. A good friend with infallible political instincts (who rapidly rose to become Chancellor of the entire ten-campus University of California system) said to me that "You probably think everything worth doing is worth doing well, don't you." "Yes, yes," the young me eagerly responded. "Wrong," he replied, "Not everything that has to be done actually needs to be done well, and if you don't learn to correctly prioritize your time you'll be a failure."

As an example, I had no choice but to sit through countless meetings during my years at the university. But, I quickly developed the skill to hear the general drone in the background as I read research papers, edited manuscripts, or did other work that was important to my career. When a certain lull in intensity happened I knew it was time for a vote. So, I paid attention for the next 30 sec. and then went back to doing what did need to be done well. In contrast, when some important task needed to be done administrators would appoint me Chair of a committee tasked with getting it done.

In the context of motorcycles, I've heard it said that someone either does quality work, or sloppy work, but the same person can't do both because sloppy work causes bad habits. That may be true for some people, but it's definitely not true in general. But, I digress...
 

Cyborg

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I think where I went wrong with the assumption was... between this thread and the other one with the picture of the Bunsen valve, I “assumed” you were using the valve with your test pipe and A/F sensor setup. I guess my new assumption based on your response is that you only use the Bunsen valve when using the sniffer?

Using your Tokyo subway analogy, when the new guy gets on, the pressure from his presence does indeed make it to the back of the car. Wouldn’t that in turn mean that an O2 molecule that had just passed the sensor get shoved back across the sensor? Back and forth like the slinky in the video.....

Sage advice from the Chancellor, but do you subscribe... a true believer? I think not given the fact that you showed up here a month later with a LMA-3 and a knock sensor to boot.

I developed the skill to deal with that general drone at an early age. Got me kicked out of school a few times due to my inability to recover seamlessly. One time in English class, the teacher had asked me a question.... I thought that I had absorbed enough of his droning to answer the question. “Jesus Christ “ I replied.... apparently it was the wrong answer and our normally semi comatose teacher went berserk and threw me out of his class. That was pretty much the end of my high school education, so if I mix up my pronoun order, you’ll have to excuse me.
 

Magnetoman

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I guess my new assumption based on your response is that you only use the Bunsen valve when using the sniffer?
That's right. I have three Gold Stars and a couple of extra header pipes in "non-concours" condition so it made sense to convert one of those. I haven't used the Bunsen valve since making this conversion since I haven't tested any non-Gold Star bikes since then. But, if I did, I'd use the Bunsen valve.
Using your Tokyo subway analogy, when the new guy gets on, the pressure from his presence does indeed make it to the back of the car. Wouldn’t that in turn mean that an O2 molecule that had just passed the sensor get shoved back across the sensor? Back and forth like the slinky in the video.
If I understand, you're worried that even though the sensor is located well upstream of the tailpipe it would triple-count any unfortunate post-combustion O2 molecules in the vicinity as they pass the sensor, are then shoved back past it in the opposite direction by the reversion wave, and then pass it a third time when they're finally headed toward their escape out the end of the pipe. While that might happen, the successive passes of the molecules are separated in time so they only get counted once at each time interval, i.e. the sensor isn't fooled into thinking the same 02 molecule is a set of triplets since it passes by the sensor at different times. Further, if "old" O2 is near the sensor it means "new" O2 from the subsequent combustion cycle can't have made it that far to enrich the O2 so at all times the instantaneous ratio of O2 to CO2 is correctly sensed.
Sage advice from the Chancellor, but do you subscribe... a true believer? I think not given the fact that you showed up here a month later with a LMA-3 and a knock sensor to boot.
" A foolish consistency is the hobgoblin of little minds." Of course, even if Emerson's observation is true, it doesn't mean inconsistency is necessarily better...
I developed the skill to deal with that general drone at an early age.
Going way off topic, it turns out I'm on the board of directors of a foundation based in the UAE. For our last meeting the plane out of DFW was delayed by mechanical problems, which made me miss my connection at Heathrow so I had to wait all day for the next one. As a result, instead of getting a full night's sleep after I arrived, I landed in Dubai shortly before the meeting was to start. I made the driver take me to the hotel for a quick shower and then to the meeting, which ended up being conducted 98% in Arabic (of which I can recognize maybe six words). Despite my jet lag and lack of sleep, or maybe because of it, I was able to follow the flow of the meeting all day (helped by a detailed agenda in English as well as Arabic), and was even able to contribute -- in English -- from time to time. Apparently, all meetings everywhere in the world are essentially the same so to serve as a committee member you don't have to speak a word of the language to basically know what is going on.
 

Magnetoman

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The first photograph shows work in progress. It's actually nearly done, but I'm waiting for another LED to arrive before drilling the final holes. Shortly after the LED arrives this will become the upgraded Mark II "universal" instrumentation package that I've designed to clamp to just about any set of handlebars. What the photograph doesn't show is brazed underneath is an array of seven nuts to allow the clamp, shown in the second photograph, to connect to the platform as close as possible to the center of gravity irrespective of the location and orientation of the clamp on the handlebars (e.g. clip-ons are nearly horizontal, the unobstructed segments of ape hangers are nearly vertical, and typical handlebars are somewhere between these extremes).

The Manfrotto "Super Clamp," repurposed from its camera holding tasks, is perfect for this. It has a rated capacity of 33 lbs. but only will be holding less than 3 lbs. including the Manfrotto universal joint. Together they can position the platform in the best location on just about any bike, as well as hold it so it doesn't vibrate any more than the handlebars themselves do.

Mounted on the platform will be an Innovate MTX-L air/fuel gauge along with a data logger that will record data from that meter as well as from a "universal" throttle position sensor (that also clamps to handlebars), tachometer, accelerometer, exhaust gas temperature (EGT) sensor, and knock sensor. As mentioned previously, engines "feel" like they're running well with Air/Fuel Ratios anywhere between ~10:1 and ~15:1 so accurately adjusting the several circuits and jets in a carburetor for either max. h.p. or max. fuel economy requires just such instrumentation.

For someone who doesn't want to permanently install a wide-band sensor in their vehicle Innovate sells an "exhaust clamp" (sampling attachment) that inserts in the end of the exhaust pipe to sample the mixture. The next photograph shows the sampling attachment that I bought with my original meter.

The design is like a Pitot tube, with the exhaust flow past the holes in the side of the shorter tube reducing the pressure and drawing the mixture in the end of the longer tube, past the sensor, and then back out again through the holes in the shorter tube. However, this sampling attachment comes with the warning that it probably won't work on a single-cylinder engine (or a twin with separate pipes) because air is sucked back up the exhaust pipe some significant distance on each cycle. Unless the tip of the sampling unit is further up the pipe than that point, it will give bogus readings. Which it does on my motorcycles. I overcame this problem with a "Bunsen valve" arrangement I discussed some time ago, but it wouldn't be an ideal solution for many people.

So, how far does air get drawn back up the pipe? Despite the relatively short pipe currently on my Catalina I know from the behavior of the meter that the location of the sensor doesn't suffer from the air reversion problem. It happens that the Catalina's "silencer" doesn't have anything in the center of it so it's a straight shot all the way to the bend in the header, just past the "permanent" sensor. Since the sampling unit is pretty much useless as-is, I extended it by 10" so it now reaches to the location seen in the photograph. This will let me answer the question at the beginning of this paragraph.

As a result of my instrumentation upgrading process I now have a second Bosch sensor and a separate control unit for it. Which means I can have my upgraded Mark II instrumentation package in place, but also use the elongated sampling unit to determine the depth into the pipe where reversion no longer is a problem. With a helper, AKA long suffering wife, I can check this from idle up to at least a few thousand rpm while the bike is sitting in the driveway. Note that I'm not suggesting determining the jetting this way, since it wouldn't be under load, only determining the depth of the reversion.

This elongated sampling unit has two separate functions: as a test probe to determine the depth of reversion, and to determine the AFR on the road without having to modify the exhaust pipe or use a Bunsen valve. However, the latter relies on the design of the silencer so it won't work on all bikes. For example, it fits up the pipes of a Matchless G80 and Triumph 500, but not a Trident. Still, for bikes where it will work it is an alternative to either a Bunsen valve or permanent modification of an exhaust pipe.
 

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