AFR info
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AFR Info
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By Stu aka S.Hanson #17,
March 8, 2021 in go faster
Stu aka S.Hanson #17
Posted March 8, 2021
I have been interested in running an afr gauge on my bikes to dial in carburation and taking the guesswork out. It is an extra safety measure and I feel worth it if you spent a lot of $ on your motor. I have never run one and have not installed one but we have discussed on the forum briefly with member Vegansydney who has experience with them. I bought a Koso wideband (for two and 4 strokes) afr kit. It is digital so it must be run with a 12 volt d.c. battery. The sensor should be run only while you set your carb up, otherwise the sensor becomes clogged with oil. It is temporary. I decided on the digital because numbers are easily seen while riding. You will also need the 2stroke sensor adapter. The afr sensor will be damaged by temps over 700 degrees without it. On the adapter there are two holes that once screwed in will sit it the exhaust stream. One on the bottom and one on the side and a small mark on the adapter so once screwed in you can tell what direction it faces. Im guessing it needs to face in the stream or away.. not sure which. You will need to cut a hole in your exhaust and weld a threaded bung (comes with kit and a cap to plug it once removed) on the hole to be able to screw the sensor in. Use anti seize or you will never get it out. If you have more than one bike you can buy extra bungs. It has been suggested to install at a 90 degree angle to keep oil collecti g on it to a minimum. It will be necessary to take off a floor board while running the afr because of the requirements of where to place the bung/afr sensor.
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vegansydney
Posted March 8, 2021
As you know I've been using wideband AFR gauges for a while now to jet the carbs on my tuned scooters and can't recommend them enough. For me it takes the guess work out of jetting. Unfortunately, I can't help with the 2 stroke adapter as mine (different brand) never came with one, but my sensor is still working after many hours of use.
Good luck, Stu. I'll be watching this thread with interest!
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vegansydney
Posted March 9, 2021
Hi Stu,
Can you please tell me the source of this table? Did it come with your wideband probe? While I'm familiar with the ideal settings and 2 stroke stoichiometric values, this is of interest as it shows the effects of the entire wideband range (AFR: 6.0:1 - 22.0:1)
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charliefentonsboy
Posted March 9, 2021
Also following this Stu, I bought the Koso set up you have a while ago, and plan to use it on my GP once its running this year.
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Stu aka S.Hanson #17
Posted March 9, 2021
Hey Benji, tried to pm you but it said you can't receive messages. The chart is a screenshot I took. Cant remember from where. Could be from a YouTube vid. Took down the charts i had up since 12.5 is what you guys said was what to aim for
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jbcollier
Posted March 10, 2021
I usually post only in the shaft-drive section ('55 150D) but I'm also running a Casa SST ('64 Li125) so I thought I would check it out here. The chart you have copied is for 4T applications (and only modern ones at that). I have used A/F-R gauges extensively to tune engines, mostly 4T and some 2T. It's an absolute miracle tool and takes the guess work out of jet selection. It's great at finding those 2T-deadly, transient lean spots. While it is good for setting up, there can be problems with sensor contamination over the long haul on 2T engine. Online reports suggest a couple of K max before the sensor dies. I run at 4% so I just use the A/F-R gauge to set it up and then remove it. If you want to monitor conditions after that, I would use an EGT/CHT as already discussed. Set it up with the A/F-R note the readings on your EGT/CHT and then you'll know when your engine goes twilight* on you.
On my SST, I run at 12.5, period. Anything above 13.0 is lean, period. Mix also cools the piston. If you are seeing 14s or, gulp, 15s, you'd better have a priest on speed dial because you are going to be burying a lot of top ends.
* zone, not vampires.
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vegansydney
Posted March 16, 2021
Great info! Completely agree with this:
On 3/10/2021 at 8:52 AM, jbcollier said:
It's great at finding those 2T-deadly, transient lean spots.
I've always aimed for 12.5:1 - 12.8:1 when setting up mine. To be honest when I first started using wideband probes I was a little shocked how much ambient air temperature and humidity had on jetting, sure you can 'feel' the difference riding in different seasons and adjust accordingly, but seeing it translated into AFR was completely eye opening to me.
I'd love to set up a probe on one of my stock Lambrettas, just to see how how far out the factory jetting is
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jbcollier
Posted March 17, 2021
A stock engine on stock jetting would be quite a bit leaner. I'd guess in the mid-13s. Stock engines are not very stressed and the cooling system is better able to deal with the heat output (more so on a V#$p@ than a Lambretta, granted).
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3 weeks later...
Stu aka S.Hanson #17
Posted April 3, 2021
First problem. Should the hole face into or away from the exhaust stream? I'm thinking it should face into the stream. Bung fits 11 to 12 inches from the exhaust flange. Example of where the bung is on new s.i.p. pipes.
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Stu aka S.Hanson #17
Posted April 3, 2021
Bracket design for koso digital afr gauge. Right side, mounting under handlebar.
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Stu aka S.Hanson #17
Posted April 5, 2021
Sorry. Here is the finished bracket. Right side, under handlebar mount. I had 10 of these laser cut out of 1/8 in. 6061 for left side westach egt/cht gauge pod. Pods getting welded to tab. When finished I'll post in the other thread. I found the koso gauge comes with the black mounting bracket that fits well on my bracket when bent for the right side.
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Stu aka S.Hanson #17
Posted April 9, 2021
Won't be long now
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vegansydney
Posted April 9, 2021
Nice work! Be interested to see how you get on with the jetting once it's all set up. Even though it still takes time to dial in the jetting, it takes all the guesswork out of the process. Personally, I could ever go back.
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Stu aka S.Hanson #17
Posted April 11, 2021
With 2 stroke sensor bung adaptor and bung plug.
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Stu aka S.Hanson #17
Posted April 16, 2021
Checking my battery, connection to the gauge. H-- is afr sensor not connected, connection bad or sensor heater has failed. Working! I won't get it on the bike for a few days. The battery is a four cell lithium I bought for my rd back in 2014. The brand is Ballistic but I dont think they make the four cell anymore. It is not ideal to run without a charging system. It can be damaged if the charge gets to low and is more for cranking a motor over to start. I really don't think it will be an issue running my sensor. It weighs under a pound. 1/2 pound maybe?
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Stu aka S.Hanson #17
Posted April 23, 2021
Installed then went for a very short ride around the block. My cold idle was 16.9 to 18. Got the bike up to 3rd. Seems in general my 1/4 to wide open is 11 to 12.5 and 1/4 throttle to idle is lean. The first adjustment will be a larger idle jet. I am running a 32 tm mikuni on an rb 225, static timing 17 btdc and I use b9egv plugs. The battery is held on with velcro.
Old notes for my starting carb jetting is
5FP17 needle highest (richest) position
320 main
389 series Q2 needle jet
20 pilot.
No air filter
Ended up with a 30 pilot. Idle fluctuates between 12.6 and 13.2. I could go to a 32.5 but it is only about 65f. out and lower humidity. I figure when it gets to 80 and humid it will be rich. Have to ride it for a few miles and see how it is.
4/25 61 f , 50% humidity. Changed from a 320 main to a 330. Moved the needle to the middle position. Seemed good at a 320 till I shifted to 4th and 5th wide open, then the numbers started to climb (lean). Seems a lot richer 1/4 to half throttle. May change to a 27.5 idle jet. Now it is on the rich side all around. Going to put more miles on it to recheck
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vegansydney
Posted April 23, 2021
Now the fun begins. Ha! Personally, I'd recommend finding a long stretch of road with a gradual incline and no traffic lights or intersections. This way you can hold it in a given throttle position for a couple of minutes under load up a hill. Preferably in the morning or early evening when the weather is cooler. Good luck! Watching this with interest.
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jbcollier
Posted April 29, 2021
Can you fit a powerjet to that Mikuni? That would take care of the leaning-out at WOT in 4th and 5th.
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Stu aka S.Hanson #17
Posted April 29, 2021
Almost positive I could, but with the larger main, it seems to have cured that issue. Its raining today, but I plan to take it out on the highway to check wide open throttle in the next day or two. I find choosing a different needle can be difficult. They are all numbered differently and its not entirely as simple as getting the next size up or down for leaner or richer. Also I might have to change my needle jet to a 389 q4 (richer)
5/2 went on a long ride. Same issue. Running lean in upper rpms in 3rd, 4th and 5th. Couldn't really push beyond half to 3/4 throttle. Felt like the motor would surge like a too rich or to lean. Afr said I was dangerous lean. At the end of the ride i adjusted the float bowl level. Will check on a ride soon. A 330 main on a 32 tm mikuni should be plenty large for a mostly stock RB22
5/12 short ride but wrung out 4th. Float bowl level seemed to be what it needed. Still a bit lean at 3/4 to WOT in 4th and 5th. Will change to a 340 and see how it goes
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jbcollier
Posted April 30, 2021
Here are some links to Mikuni needle charts:
https://www.jetsrus.com/a_jets_by_carburetor_type/needle_mikuni.html
http://www.nichecycle.com/ncs/categories/carburetor/mikuni-parts-by-category/jettting-tuning/needles.html
https://www.mikunioz.com/shop/jet-needles-6-series/?v=3e8d115eb4b3
Degree your throttle with tape and a felt pen. Note the throttle position where in the mid-range there's an issue and then you can check what part of the needle is exposed at that throttle setting.
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3 weeks later...
vegansydney
Posted May 20, 2021
Hows the dial in process going, Stu? Any luck?
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Stu aka S.Hanson #17
Posted May 22, 2021
Ha! So remember how I was confused by the correct afr readings half throttle and less and it would go terribly lean at high rpms? Blew a head gasket. So irritated.
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