Wideband sensor for Air/Fuel Ration (AFR)

[higgy]

not quite right, the heat source is not to get them to ideal operating temperature but to boost their activation time. The sensors only start working when they reached min 250-350°C.

picker of nits

[romus]

I'm truely tempted........ as long as my bike is not running smoothly, overall in low rpms range or starting after a red light.
But the Wideband a/f gauge is only one of the parts.
I need also the manual of the weber carb to know where to touch in order to obtain the best response to the gauge. I have never had my hands on a car carburator installed on a bike.
I apologize for my ignorance, but just to know, if the value is too low, means poor moisture or rich moisture?

I've been where you are at. I am not an expert compared to some of the guys on this site but I did do a lot of work on my Weber and now I am trying a Mikuni wondering what the difference may be. Others have put in FCR's. I'll have a go at explaining the AFR thing.

Let's say 12.8 Air Fuel Ratio (AFR) is a perfect goal for the Paso. I think it is. Think of that as a base line. That means 12.8 parts of air to one part petrol/gas.

If the AFR reading was 10.0 that would mean 10 parts of air to one part petrol/gas - that means there is less of a percentage of air and more percentage of fuel/gas, which is a richer mix (rich in gas). A quick throttle wind up from the lights would probably show an AFR 10.0 by the way, with the Weber, because there is a thing called an accelerator jet that squirts extra fuel if you do a quick throttle wind up (because the engine is gasping for a chunk of rich fuel at such a time). Actually I think 10 is too rich - I reduced the size of my accelerator pump jet so it would only drop to high 10s-low 11s.

If the AFR reading was 13.8 that would mean there were 13.8 parts of air to one part of gas - that means there is more of a percentage of air, which is a leaner mix. Well 13.8 AFR, is probably what you would see, with the Weber, when driving at a motorway speed up a hill incline, because the factory setting of the Main jet is pretty lean - I think for fuel economy and noise reduction (more air in the mix means less fuel, so that's cheaper and a lean mix is not quite as noisy as a rich one).

Air isn't just air either. Air thins in hot weather and as you increase altitude, so lets say your bike is running nicely during winter but not so well in summer (when the air is warmer/thinner). An idle that was 12.8 in winter might be 13.8 in summer. So maybe your idle mixture screw needs a little tweak and/or, if it's really out, a different idle jet (the idle mixture screw is the last fine tuning step).

When you're idling at the lights, the petrol in the Weber is running through the Idle jet. The first possible problem is if your idle is too rich e.g., AFR 11.5. In this case when you take off from the lights the carb squirts some extra fuel from an accelerator pump jet. If your idle was 11.5 the squirt might take it to low 9s or 8s AFR, which would stumble the engine. Okay, so you take off from the lights and it might cough after a bit too because there is a bit of starvation going on once it's used up the squirt. Also if there has been no opening modification to the airbox, there might be a bit of starvation for air, adding to the problem. After the engine has used up that squirt of fuel (or when it is just about used it up) there is a transition going on from the Idle jet to the Main jet, meaning the fuel starts to flow through the Main Jet and not through the Idle jet. With the Weber this is a traditional 'lean spot' and tuners do a lot to try and take that lean spot out: maybe increasing the Main jet by one size would fix it, increasing the float bowl level so that the fuel is transitioning just that little bit quicker. Even the jet that lets the fuel into the Weber float bowl can be swapped for the different type called a Gross Jet. The Weber too connects to manifolds of different lengths so there is the need for some slight difference in jetting for each cylinder to adjust for this.

There is a complication too with a thing called an ET tube where the air and fuel mixing goes on. The ET, without modification, creates a span difference of, I think it's, 3 AFR between idle on the rich side and when the engine is pulling on the lean side. That means it's hard to get the idle at a good AFR without getting an overly lean and hot engine when there is pull on the motor. I think this is another Weber idiosyncrasy that probably is not an issue for cars but creates some issues for a bike. That span can be reduced or evened out with some modification to the ET.

If you are working on any or all of those ideas, having a Wideband sensor and controller would be a super asset because it can clearly show you the points where there is an issue and you can focus on making changes there. So, if you can say you are getting a lean spot at 3000 rpm and what the AFR reading is then people know how to advise you etc etc. But as you see you can easily end up playing with more than one part. The value a Wideband sensor and controller is the same no matter what carb you have.

And you are right that the carb jetting is only one part of the issue. Apart from the air box and vacuum balancing of the carbs, the cam timing might be off (in my case before correcting the cam timing I needed an odd jetting difference to get matching AFR for both cylinders). The factory coils aren't the best and the wiring to the coils also is not so good. I would definitely change the coils if you still have the originals and do the coil wiring mod. Those changes alone could fix your less than smooth running symptoms because maybe your carb settings are okay.

Higgy and I made a manual for a Weber mod. That and other manuals can be down loaded from "750 Paso discussion>Paso magazine articles and other downloads"

[paso750]

nice writeup, Warwick. I hope you don`t mind that I add something for the guys who might be interested but are on a budget or don`t see the benefit of getting an LC-2 or the more expensive LM-2 if they only plan to do some adjustments on the Paso once or twice.
There are cheaper solutions that are of course not that sophisticated, but that`ll do the job.

But it can be done even cheaper and all you need is the weld-in bung, a sensor and a voltmeter.
If it`s in working order a used sensor will do fine. It should be one with 4 wires. Two are for the heating, two for the sensor. The manufacturer is not relevant. (the one I`m using is either from my old Fiat Tipo or Audi)
Find yourself a shop that does emission tests, who have an LM-2 or similar equipment.
Set your voltmeter to a low voltage range (i.e. max. 5VDC) and connect it to your sensor. (in parallel to the equipment the shop is using to read the sensor output).

With the engine at operating temperature and at idle adjust the mixture adjusting screw to first 11.8 (0,8La) and write down the voltage from the voltmeter or make a mark if you use an analog instrument. Then do the same for 12.5 (0,85La), then 13.2 (0,9La), then 14 (0,95La). More values are not need, but of course you can write down a few more.
Now you have your own AFR meter.

"La" means Lambda, which is the value we`re mostly using here. For a theoretical full coming burn you need one part of gasoline and 14.7 parts of air. Lambda is the value of supplied air in relation to the theoretically required amount of air. (hence La=AFR/14,7) See table below.
Just forget this info if it`s not relevant for you. I don`t intend to cause any confusion.



The global-tuning takes place basically in driving, because on a test stand only the full load (full power) area is tuned.
An engine has it`s max. performance with approx. 0,88La to 0,90La (rich mixture). The engine has smallest consumption with still acceptable running culture (smoothness) with approx. 0,90La to 0,95La. When accelerating it should be 0,8La, in order to receive a spontaneous acceleration.
With Lambda 1.0 to 1.1 the engine has the smallest pollutant proportions with smallest gasoline consumption, but also a smaller performance with increased gasoline consumption, with increased engine temperature and particularly with miserable runnig culture. At values under 0,7La (very rich) or over 1,2La (very lean) usually the ignition boundary is achieved; the engine stutters.

I do recommend to put some ceramic paste on the sensor plugs to prevent them from seizing.
It doesn`t happen that often but a few guys already lost one so it`s not a bad idea to have them drilled or just saw a small groove in the head and secure them with safety wire.



About the jumpy indicator. Doesn`t the LC-2 or LM-2 have a sensivity adjustment ?

G.

[sergiomala]

Thank you guys,

I learnt more in a few posts of this forum than in all my long life

I'm clearing my mind, and hopefully next to take some decision.
I will try with weber carburettor first. I do live in Italy, and i hope this might help somehow.
If i miss the goal i will look for a carburetors swap.

Thanks again

Sergio

[jayh]

For general afr ratios at fixed rpm's the lm2's are a very usefull tool,but for very quick changes in afr (like the paso weber issues), you will find them lacking in response time.Even with the benifit of rpm and chrono mapping, the problems are still very hard to isolate precisely. J.

[higgy]

data can be adjusted in the program.

[Tamburinifan]

A/F logging under load is still needed to get you in the right
neighbourhood of how to adjust jets/air etc.
Reading A/F IRL is just guessin...

My 2c.

[jayh]

Just thought of something that clarifies my last post which was a long time ago.
The weber problems happen very briefly,whilst under acceleration.This is not a situation that can be continued by holding the throttle at a certain position.It happens and is gone within a second or two.
The lambda meter does not get a true reading of what is happening as the duration is too short.
lambda meters take several seconds to adjust to their true reading.
I hope this helps. J.

[JWilliam]

This is great stuff Warwick. I must say, I have always thought the air-corrector jet idea to be over rated. Standard setting is as big as the main jet. I dropped it to 90 and increased the mains to 180. I mean, your regular flat slide doesn't have anything like that so I figured at high rpm the Paso has a chance of running lean and I tried to get back to more traditional fuel feed concepts. When the AC jet was blanked it had some stutter on throttle opening so I guess it has some use. It certainly complicates the arrangement.

[paso750]

I can`t say how fast that Lambda/AFR meter on ebay reacts. Some may react quicker than others. I know mine has a sensivity adjustment. However while instruments like an LM2 or others with datalogging and more functions are great tools not everyone is willing to spend hundreds on them just to fiddle with the carbs every now and then. A lambda/AFR meter like this is an inexpensive and imho sufficiant option for the occassional user (which is probably more than most forum members here are).

[jayh]

Please dont get me wrong,the lm2 and other cheaper meters without data logging,are very accurate instruments,and will show you a correct reading for most uses,but for split second readings,they only show the readings in the seconds leading up to the problem,and the seconds after.It is very difficult to get a definitie answer to what is happening at the precise moment as the reaction time is too slow.
For measuring readings under constant throttle conditions ,they are brilliant.
J.

[paso750]

There`s one thing I`m wondering about and I`m asking the following out of ignorance: if there is one of these brief moments which you can identify only in a datalog is it really possible to make a change on the carb to make an improvement at the exact point? I understand that on an injection system you can check the mapping and do a modification exactly there were the problem occurs but a carb imo has always been a rather unprecise instrument.

[jayh]

That's right G,Carbs are rather imprecise,and the point at which a problem occurs can change,due to gear
selections,throttle positions,terrain etc.That is why mapping is so effective,because different maps can be
made or computed for things like throttle position gear selection,and injection and ignition timing adjusted to optimise power delivery for different scenarios such as street,wet weather,or sports modes.

My work on the weber used the LM2 to identify where to start looking and then hundreds of adjustments/tests were conducted to 'feel' the differences.After a while you can tell if the changes are
helping from the way the weber behaves when cold,and learn what to expect from it once warm. J.

[higgy]

G Only Direct injection is capable of making changes that are not blanket corrections. Direct injection can make changes faster than the individual power stroke especially the 24 volts systems. Sequential injection comes close but still is a blanket correction. Electronic mapping is only limited by memory, Clock speed and speed of the injectors. Carbs could have been made to compete but why bother with such a complex and expensive option