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Author Topic: 02 sensor for tuning carbs?  (Read 425 times)

Offline k.graham

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02 sensor for tuning carbs?
« on: Feb 03, 2019, 13:12:51 »
Has anyone here ever tried rigging up an o2 sensor into your exhaust to try and get carbs balanced and tuned? I know this is a thing when it comes to tuning carbs on classic cars. Wondering if anyone here has tried it on their bike? It would require welding a nut into each exhaust stream youíd want to isolate, but as far as I can understand itís possible to rig up with a standard 02 sensor and a multimeter. Anyone have any experience with this? I feel like this would be the most consistent way to dial a set of carbs in and not have the hassle of doing ignition chops and reading the plugs... it seems like itís not commonly done though, so is there a reason this hasnít been adopted for tuning up a bike?

Offline irk miller

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Re: 02 sensor for tuning carbs?
« Reply #1 on: Feb 03, 2019, 14:16:51 »
Yes.  A bunch of guys do it.  The member trek97 on here did it on his 360.  If you dig through his 360 thread, you see plenty of details for his process.  He has all his carb work well documented in that thread. 

http://www.dotheton.com/forum/index.php?topic=27417.1040

Offline der_nanno

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Re: 02 sensor for tuning carbs?
« Reply #2 on: Feb 03, 2019, 18:07:39 »
Did it in the past on the turbo and will do it on my next (new) exhaust for my Yamaha XV, just to get more reliable data by using a wideband.
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Offline teazer

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Re: 02 sensor for tuning carbs?
« Reply #3 on: Feb 03, 2019, 19:15:23 »
You can weld a bung into each pipe and block off the cylinders that you are not reading - and use a single wideband sensor.

That's the easy part.  Just some work and cash.  The hard part is working out what lambda or A:F ratio you are looking for under different conditions of load and throttle setting.

An easier way is to strap it to a dyno with exhaust sniffer and let the dyno operator help to get the jetting right.  We talk about a ratio of 14.7:1 but that's rarely what we are looking for.  For best power it needs to be closer to 12/13:1 and for best economy closer to 16:1.  Your dyno guy should be able to point you in the right direction.

Offline trek97

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Re: 02 sensor for tuning carbs?
« Reply #4 on: Feb 03, 2019, 20:17:54 »
My 76 Honda 360 is happiest at approx 12.8 to 1 mix at idle and cruising.  Can go leaner during acceleration- up to 14-1. 
Most power without the fear of overheating, as its air-cooled.
You can go leaner if your machine is liquid cooled.

Installing O2 sensors is an awesome tool for tuning.

« Last Edit: Feb 03, 2019, 20:25:30 by trek97 »

Offline teazer

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Re: 02 sensor for tuning carbs?
« Reply #5 on: Feb 04, 2019, 01:00:58 »
https://x-engineer.org/wp-content/uploads/2017/10/Engine-power-and-fuel-consumption-function-of-air-fuel-ratio.jpg?b407ec&b407ec

https://www.enginebuildermag.com/2008/07/carburetor-tuning-the-airfuel-equation/
That suggests Idle at 13.4 -14 :1,  Acceleration at 12.5:1 and cruising at the same as idle. 

What we found was run teh motor on a dyno and test the gas for AFR etc and see what AFR corresponds to peak HP and if atmospheric conditions change, go back to the peak power AFR by changing jets.  In reality, once I find a good jetting baseline, I tend not to change it.


Offline Rat_ranger

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Re: 02 sensor for tuning carbs?
« Reply #6 on: Feb 04, 2019, 04:42:02 »
An inexpensive but decent wideband is the innovate mtx-l.  I've had one on my triumph spitfire to help tune the dual SU carbs, to now telling the ECU how to adjust the EFI.  Ultimate set up would be a data logger that has rpm, throttle position and wideband.  That way you know exactly what you were doing and where the adjustment needs to be.

Offline trek97

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Re: 02 sensor for tuning carbs?
« Reply #7 on: Feb 04, 2019, 07:59:57 »

That suggests Idle at 13.4 -14 :1,  Acceleration at 12.5:1 and cruising at the same as idle. 


If I take the old 360 any leaner at idle the rpms drop.  Thats how I found 12.8-1 ratio.  Just tuned for fastest idle, as per manual and voila.

Offline k.graham

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Re: 02 sensor for tuning carbs?
« Reply #8 on: Feb 06, 2019, 00:32:43 »
Thanks everyone for the info! I found a single wideband setup for $100 on kijiji, so Iím going to give it a try!


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