help plz. wideband afr fine tuning the carb

[MikeJames21]

ok first i have a full exhaust, k&n pod filter w/ stock runners and factory pro stg 3 jet kit.
basically when i did the jet kit, i just did what other ninjettes did w/ full exhaust/pod filter and its ran great.

i just got an innovate mtx-l wideband to monitor my afr's, so i could see how it's really running and fine tune it from there.


i found this chart right here...

Air/Fuel Ratio Limits
6.0:1 Rich run limit
9.0:1 Low power, black smoke
11.5:1 Rich best torque at WOT
12.5:1 Safe best power at WOT
13.2:1 Lean best torque at WOT
14.7:1 Chemically ideal
15.5:1 Lean light load, part throttle
16.2:1 Best economy, part throttle
18-22:1 Lean run limit

basically, i'm confused on what my idle afr should be. right now, after warmed up, etc.. it will be around 17.5-18.5 sitting at a light idleing.
shouldn't the idle afr be closer to 14.7??

cruising the speed limits it reads around 13.8-14.8
WOT = 11.8-12.7 (last night coming home on hwy it was 12.6 steady at WOT)

im not sure what to do.. haha, any help would be much appreciated.


i took a video yesterday, should be uploaded soon.
http://www.youtube.com/watch?v=CUeYy...ature=youtu.be

[alex.s]

the idle air mix screws are behind two caps marked with white dots on the carbs. drill and pull the caps then adjust the idle screws with a small flat head screw driver.

[MikeJames21]

ive already did that, when i put the jet kit in... but i just did what others have done and it was october last year, i haven't messed with them since, it's ran great.
now that i have a wideband i can see the afr's and i want to know if my idle afr should be 14.5ish? not 17-18?

everyone on a local forum for cars/trucks/bikes is basically saying my afr's are basically spot on, and that the 17-18 idle is fine. and not to mess with it unless i want to try to get a little more power..

free dyno day saturday here, i will probably be going!

[alex.s]

Originally Posted by MikeJames21

ive already did that, when i put the jet kit in... but i just did what others have done

i'm confused. are you saying you took someone elses recommended setting and set it to that instead of actually tuning it correctly to your bike?

the way you tune the idle mix screw is set it to the position at which it idles the highest, then set the idle to spec.

jetting changes a lot because the atmosphere you run the bike in changes a lot. it depends on current temperature, altitude, humidity, carb internal passage gunk. all kinds of stuff. even if you did jet it correctly a year or whatever ago, it easily could be out of tune currently.


it doesn't make any sense to me not to have your idle mix correct.

[DaBlue1]

Originally Posted by MikeJames21

....now that i have a wideband i can see the afr's and i want to know if my idle afr should be 14.5ish? not 17-18?

....everyone on a local forum for cars/trucks/bikes is basically saying my afr's are basically spot on, and that the 17-18 idle is fine. and not to mess with it unless i want to try to get a little more power..

Probably should have used this thread as a guide for tuning the AF/R on the Ninja 250.

[MikeJames21]

alex, when i put the jet kit in i went to the jetting database to see what others w/ full exhaust, k&n pod filter did. and it's ran great... now 8 months later i have a wideband and can see my afr's they are basically spot on.

i will do this idle air mixture you are talking about, but i still want to know what my afr should be at idle..

dablue1: i read 3 threads like that, in the aem wideband rental thread. no one is saying what there afr's are at idle.

[greg737]

Where is your wideband O2 sensor mounted?

I'm surprised to see you list your idle air/fuel ratio as being 17.5 to 18.5. That doesn't seem right. I can't imagine that the bike's Keihen carbs are actually delivering that lean a mixture, especially when you say that you've removed the idle mixture plugs and adjusted them to the recommended 2.5 turns out.

With that setting I'd imagine it's actually idling at 13.5 to 14.5 afr. For your engine to react well to rapid throttle opening from idle speeds it has to be somewhere in that area. If your engine was really at 17.5 afr there would be a moment of hesitation (or even a stumble) when you rolled on throttle from idle.

If your O2 is mounted near a connection point in the exhaust system or too near the exhaust cannister or, worst, mounted in the exhaust cannister itself then there's a chance that you're getting fresh air leak-back at idle which would cause an error in the O2 sensor reading. Also, if there's any chance that the O2 sensor is cooling off too much during idle it can give messed up readings.

[MikeJames21]

Originally Posted by greg737

Where is your wideband O2 sensor mounted?

I'm surprised to see you list your idle air/fuel ratio as being 17.5 to 18.5. That doesn't seem right. I can't imagine that the bike's Keihen carbs are actually delivering that lean a mixture, especially when you say that you've removed the idle mixture plugs and adjusted them to the recommended 2.5 turns out.

With that setting I'd imagine it's actually idling at 13.5 to 14.5 afr. For your engine to react well to rapid throttle opening from idle speeds it has to be somewhere in that area. If your engine was really at 17.5 afr there would be a moment of hesitation (or even a stumble) when you rolled on throttle from idle.

If your O2 is mounted near a connection point in the exhaust system or too near the exhaust cannister or, worst, mounted in the exhaust cannister itself then there's a chance that you're getting fresh air leak-back at idle which would cause an error in the O2 sensor reading. Also, if there's any chance that the O2 sensor is cooling off too much during idle it can give messed up readings.

my 02 sensor is right after when it goes into one, basically where everyone else has put theres.

my afrs under load are where they should be, some people are saying my idle afr is fine... now i'm really confused.. should my idle afr be 13.5 to 14.5???

besides full exhaust, k&n pod, factory runners.. removing kleen air system.. i have
factory pro 112 jets, FACTORY WARM UP JETS, needle on 3rd clip, 2 turns out, might be 2.5...

[DaBlue1]

Originally Posted by MikeJames21

...dablue1: i read 3 threads like that, in the aem wideband rental thread. no one is saying what there afr's are at idle.

I think you missed the info contained within the thread. There's a couple of pictures with the AF/R readings at certain rpms as well

Your AF/R should below 14.7:1, between the 12:8:1 - 13:4:1 range @ idle/low rpms speed. (the 14 range would be at the top end)
http://www.ninjette.org/forums/showp...8&postcount=17
Also refer to this thread as well Motorcycle Carburetor Theory 101

Essentially the bike will be richer @ idle with the choke on, once warmed it will lean out a tad. Under acceleration and shifting the AF/R may spike but should come back down. At about 6k it may be in the 14.x:x range and should dip from there as the rpm goes up and you go WOT.

[MikeJames21]

ok guess i did miss that... why is my afr's spot on everywhere but idleing?
did you watch my youtube video. alls i need to do is figure out the idle afr...
should i just reset the idle air mix screws?? if so,

"the way you tune the idle mix screw is set it to the position at which it idles the highest, then set the idle to spec."
^--- set the screws til it idles highest, then turn the knob to get the idle back down to 1k-1500k rpm?

[greg737]

I watched parts of your video, the bike runs great. With regard to the wideband O2 system here's a couple of questions...

First, what is the bike's idle speed? It sounds low, like 1,300 or maybe even a bit lower.

I noticed that before startup your display was reading 22.4 afr. Free-air atmospheric oxygen is right around 21 percent. When was the last time you did a free-air calibration of the O2 sensor?

I have an Innovate O2 system (the LC-1 model) installed on my EX-250 and it reads 21.8 when I switch the key on. If you aren't properly calibrated your readings will be off or skewed (which is to say that it might be accurate or close to accurate at some points and off at others).

At 5:30 (exactly) in your video you are idling at a stop. At 5:31 (exactly) you've just begun to move the throttle to start forward. In less than 1 second the afr goes from 18.5 to 11.5 afr. It almost seems like there's something going on beyond a simple exhaust gas mixture change. It makes me wonder if your EX-250, idling pretty low as it seems to do, may not be producing enough electrical power for the Innovate system to produce a correct measurement.

[DaBlue1]

Originally Posted by MikeJames21

...."the way you tune the idle mix screw is set it to the position at which it idles the highest, then set the idle to spec."
^--- set the screws til it idles highest, then turn the knob to get the idle back down to 1k-1500k rpm?

Start by re-checking and setting your idle mixture screws 2.5 turns out, warm the bike then set the idle speed to about 1500k. Your idle speed sounds a little low. You need the engine speed up to help pull in air and fuel. How's your AF/R with the choke on when the engine is cold?

[cuong-nutz]

Originally Posted by DaBlue1

Start by re-checking and setting your idle mixture screws 2.5 turns out, warm the bike then set the idle speed to about 1500k. Your idle speed sounds a little low. You need the engine speed up to help pull in air and fuel. How's your AF/R with the choke on when the engine is cold?

Yeah, bike sounds like it's idling really low. Set your idle for 1500 as mentioned.

[greg737]

yeah, thinking about it a bit more I believe @DaBlue1 and @cuong-nutz are right that your first step should be to set the bike's idle at about 1,500 rpm. Bottom line, the carbs need to have enough airflow to function properly.

A really low idle may inhibit fuel delivery due to airflow that's simply too low for the carb to function as designed. It could be that you actually do have the idle mixture screws set perfectly but you're idling so low the carbs can't flow the fuel due to lack of engine vacuum.

[ninja250r81]

increase the idle

check the afr when riding around with the choke on.

does you headlight dim and then power-up with each pulse of the motor???

1:30 the idle is too low for a reading and this will mean the alternator will not be producing enough power to read the sensor voltage correctly.

the bike is tuned ok, even at back off at full throttle.

the low to mid range needs to be a little richer, than it would be pretty good.

richen the idle might do the trick

[alex.s]

Originally Posted by ninja250r81

this will mean the alternator will not be producing enough power to read the sensor voltage correctly.

shouldn't any decent quality gauge that was input voltage dependant like that have the sensor and reader unit on their own isolated and regulated 12v line?

[MikeJames21]

Idles usually at 1200 or so, I will raise it up and see what it does. Idle screws I will play with. Etc.
I have the wideband tapped into a cig lighter I have to charge my phone. It is ran to the battery and hooked to a switch.
I also have hids and always have brights on, plus the idle being low... I get what you are all saying
I will be worg on the bike tomorrow and will report back.

Thanks for the help guys!!
Posted via Mobile Device

[MikeJames21]

all is good now, set the idle to 1500 like you guys said. then instead of the typically 2.5 turns out on the idle mix screws i am now closer to 2 3/4-3 idle afrs are in the 14.5 range. all my other afrs richened up a little bit, so yes all is good.
seems to take off smoother from a stop, and slowing down to turn and then rolling back on the throttle feels smoother too. YES!!!

[alex.s]

every bike is different. every location a bike runs in is different. always tune the bike to the conditions, dont just use a preset recommended value.

glad you got it resolved.

[MikeJames21]

thanks for the help alex

[greg737]

That proves it, you can actually get good advice off the interwebs.