Portable Wideband AFR (Air/Fuel Ratio) Gauge

[1018cc]

I've had a request in another thread to show off my portable wideband AFR for helping to tune carbs and picking / verifying jets:


I'll be honest up front - this isn't my idea. Someone else on another forum I'm on mentioned it and posted a pic of his and I've refined his design to make this one for me. So this isn't a 1018cc original but a refinement of what I've seen elsewhere (which I'm sure some of you guys will refine what I've done too).

I'll let the pics do the 'talking' but basically, don't use a narrowband (i.e. the cheap ones you find in most cars. They are only accurate at stoich (14.7:1 for petrol) and their accuracy drops off massively either side of that. If you are going to do this, spend the money and get a WIDEBAND O2 sensor / gauge. Mine measures as rich as 10:1 and as lean as 17 or 18:1 (I can't remember but leaner than you'd want in a petrol engine anyway).

I decided on a AEM UEGO Gauge Kit (4110). I liked the look and it also uses the newer style O2 sensor (the Bosch LSU4.9 which doesn't require free air calibration to be accurate). The older 4.2LSU style occasionally needs free air calibration to be accurate. The newer 4.9 style contains a microchip in sensor that is factory calibrated (which means you need to be careful and not drop it / connector etc when moving it around).

The rest of what I put together is pretty simple. A jiffy box (grey thing) to mount the gauge in, some alligator clips to connect to battery terminals, a cigarette lighter, a hook, a RJ11/12 jack (only for data logging), wiring, 32mm pipe, some 12mm solid square bar, some flat bar, a nut & bolt and an SPST switch I had lying around in a box. You'll also need some drill bits / files etc for drilling and mucking with the jiffy box. I also added some hose clamps either side of the cables because I couldn't be bothered going back out to buy some proper strain relief when I made this.

The exhaust clamp I made myself (the AEM UEGO kit comes with a bung to be welded into your exhaust headers) but if you don't have a welder / grinder to make the clamp yourself you can exchange legal tender for a much more professional looking one that does the same job as mine for more money: http://www.ebay.com/itm/Innovate-3728-Motorsports-Exhaust-Clamp-Fits-LM-1-LM-2-LC-1-LC-2-Modular-/262043331460?hash=item3d02ffeb84:g:eUsAAOSwiLdV8byR&vxp=mtr. You will just need to check the threads as the one I linked is made by innovate and they reference their own gauges (I think the sensor thread is something like M18x1.5). As the ebay link mentions, Innovate also make their own range of wideband gauges. Pick whichever one you think will suit your needs best after reading all of the marketing garbage - the making it portable part isn't dependant on brand. I have a welder and I didn't want to pay $120AUD for something I could essentially make from scrap I had lying around (I also own a welder, chop saw and grinder which made the decision easy). The sensor can still be undone and threaded into a bung in an actual exhaust system too if that takes your fancy. This is essentially just a wideband gauge that goes in a car except I've put it in a jiffy box with some long wiring coming out the bottom so I can move it around.

I think the pictures are pretty self explanatory so I won't go into too much detail but the wiring isn't that hard. It is mostly the standard harness that comes with the gauge except I've spliced into the power feed to the gauge for the on/off switch. I've also wired it for data logging so I can log the AFR with my laptop but this isn't needed for the gauge to work if you just want something basic.



^ I made two different types of connectors. One for connecting straight to the battery by alligator clips and the other from a cigarette lighter. I've put a different connector on each end so they only plug together one way - don't want reverse polarity issues. I also put a fuse on the positive alligator clip, check your cigarette lighter adapter - some of those have a fuse built in.


^ Power connection for the above photos










^ This stuff is for data logging. I have com port to USB adaptors for the gauge, the one bundle that looks like a black wire is actually a USB borescope so I can tape it into the airbox and see the slides on carbs move up and down and the other COM to USB adaptor is for an engine management system I run on my ute (it gives me RPM, engine load, ignition advance etc - NOT USED for the GS500).

My homemade exhaust clamp. It is about 500mm long with the sensor in the centre. I used the same size pipe to make a protector for the sensor when I shove it up an exhaust pipe. I know it looks long but you don't want it too short. Engines don't push a lot of air at idle and the gauge will read max lean if air comes back up the pipe until the revs pick up. I've found this length to be about the minimum you'd want - unless of course you are more interested in mixtures while moving and the engine is at higher RPM. This problem doesn't exist when these gauges are installed in the headers. Obviously it is pretty long when in a bike exhaust so the clamp has to be good. I've made the clamp long and strong so that I can place it on car exhausts without scratching the chrome tips. If you are only interested in bikes, then I guess you can do something different. The hardest part for a bike is deciding where / how to mount it depending on how particular you are with your paint.








I won't go into detail how to use it and what AFRs to look for - I'll let you use google on your own. You need to understand the different circuits of these carbs and how all the adjustments affect different throttle openings etc. Heaps of reading there but unless you do that reading - you'll never get anywhere with changing stuff in the carbs. I usually end up helping friends / relatives tune their carbs because I have all of this cool stuff and understand carbs (which actual mechanics these days aren't taught about enough). In my opinion the BIGGEST reason carbs get a bad wrap from people as being unreliable, crappy, not as good as FI etc is from being 'tuned' by owners / mechanics that HAVE NO IDEA / DON'T UNDERSTAND WHAT THEY ARE DOING and make changes at random - when they don't work perfect it must be the 'crappy carbs' that are the problem. Carbs are simple when you understand how they work.

If you have any questions - ask away and I'll do my best to answer them if you are interested in making something like this for yourself.

[The Buddha]

This is useful for tuning @ idle.
To really tune it on the road, you're gonna have to get simpler. Much much simpler.

Mark throttle positions on the grip/switch assy with white paint/nail polish etc.
You're gonna need a digital multimeter - DMM courtesy your neighborhood harbor fright. Then pull a 1 wire O2 sensor out of the nearest crappy car (I used a 1992-94 chevy cavalier cos I did this in 97-98 and hence I don't have pics)

Then you screw that into the exhaust right ahead of the footpeg in the header.
Then wire up to the DMM which you can ziptie/Velcro to the tank/dash/triple clamp etc.

Put DMM in milli volts and over 500 = rich under - lean. Throttle position determines what jet is the influencing factor, so nearing WFO = main, 1/2-3/4 is needle etc etc. The road/highway is your dyno. Find a nice open stretch and experiment away.

Cool.
Buddha.

[1018cc]

As you say, you can always weld a bung into the exhaust if you want to screw an O2 sensor straight in. You can buy something like this and just put the plug in when you aren't tuning. People could always buy one of those cheap 52mm gauge brackets and bolt the actual gauge into one of the mirror bolt holes and that way it is on the bars and no velco / tape / bungee strap needed. Just remove it after you're done.

Getting a second hand narrowband O2 sensor is definitely cheaper but I gave up as I think it got too hard to determine accurate AFR readings on the fly (too much thinking for me). If you look at this chart:
a very small change in the mV reading means a large change in AFR reading. Easy to tell if it is rich or lean either side of stoich but I wanted something easier than that. I just wanted a display that would tell me a number straight away that meant something to me rather than having a mV reading. Just depends on how you want to do everything.

For my solution I just chuck everything in my tail bag and go for a ride and check the data log later after I've done some short runs. As you say Buddha, need to use the same throttle openings, same speeds / gear etc to get it consistent. No good changing the variables each time you go for a test otherwise your tests are useless to know if your changes are getting better / worse.

Edit: I should say that the standard wiring that comes with the gauge is super simple. Just need to put some kind of connector on the +ve and -ve for power / ground and the rest plugs and plays straight from the kit. Add some zip ties to keep the wiring where you want it and you're away.

[The Buddha]

Actually on a bike with fixed jetting you're never going to be close to that perfect point ... you're going to be in the .75 volt range and you drop 1 size and you'd be in the .25 range.
Besides a GS is also cooled by the intake charge. Getting in a nice rich mix also cools it well. You make more power if you're in the .25v range, but you're also going to be running hot.
Cool.
Buddha.

[1018cc]

Sorry, another post. If you wanted to do what Buddha is saying - I've just found this: https://www.amazon.com/Digital-Multimeter-Temperature-Bluetooth-Interface/dp/B010Y71G1K

A data logging DMM that has bluetooth connectivity for pretty cheap (for what it appears like anyway - I haven't used one). Could have your phone mounted in a phone mount on the bars displaying the mV reading via bluetooth and the DMM could be zip tied to the rear grab rail or somewhere else where you don't have to worry about scratching your paint etc.

Many ways to do the same thing. I just want to get those thoughts going through peoples heads.

[1018cc]

Actually on a bike with fixed jetting you're never going to be close to that perfect point ... you're going to be in the .75 volt range and you drop 1 size and you'd be in the .25 range.
Besides a GS is also cooled by the intake charge. Getting in a nice rich mix also cools it well. You make more power if you're in the .25v range, but you're also going to be running hot.
Cool.
Buddha.

Completely understandable and makes sense to me.

I mostly use my gauge in cars which is why I built mine the way I have. If you were going to just run one for bikes you could make one to suit your needs.

[The Buddha]

Sorry, another post. If you wanted to do what Buddha is saying - I've just found this: https://www.amazon.com/Digital-Multimeter-Temperature-Bluetooth-Interface/dp/B010Y71G1K

A data logging DMM that has bluetooth connectivity for pretty cheap (for what it appears like anyway - I haven't used one). Could have your phone mounted in a phone mount on the bars displaying the mV reading via bluetooth and the DMM could be zip tied to the rear grab rail or somewhere else where you don't have to worry about scratching your paint etc.

Many ways to do the same thing. I just want to get those thoughts going through peoples heads.

How would that "record" throttle position.

The only way to do it regardless of whether the DMM can record or not is to look at it as you hold the throttle position as well as when you open it and let it rev up under load etc etc. Essentially ride it and glance at it like you look at your speedo/tach.

Don't drag this 1972 technology kicking and screaming into 1995. It doesn't want to.
Eyes, hands, feet and butt are what it can use, bluetooth to a GS is likely a condition you will have to ride the GS to the nearest dentist.

Cool.
Buddha.

[1018cc]

Sorry, another post. If you wanted to do what Buddha is saying - I've just found this: https://www.amazon.com/Digital-Multimeter-Temperature-Bluetooth-Interface/dp/B010Y71G1K

A data logging DMM that has bluetooth connectivity for pretty cheap (for what it appears like anyway - I haven't used one). Could have your phone mounted in a phone mount on the bars displaying the mV reading via bluetooth and the DMM could be zip tied to the rear grab rail or somewhere else where you don't have to worry about scratching your paint etc.

Many ways to do the same thing. I just want to get those thoughts going through peoples heads.

How would that "record" throttle position.

It doesn't. I merely found it so you could see the display at the bars on your phone. Either way you're still relying on your hand to modulate the throttle to the same position etc - just the same if you were to tape a DMM to your bars.