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Using an O2 Sensor to tune carbs?

Discussion in 'XJ Technical Chat' started by MrSeca, Nov 2, 2020.

  1. mlew

    mlew Well-Known Member

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  2. joejr2

    joejr2 Active Member Premium Member

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    I'm probably not understanding correctly, but, do any of the gauges shown have probes that will
    fit the tapped test holes Yamaha has provided at the bottom of each header ?
     
  3. dkavanagh

    dkavanagh Well-Known Member Premium Member

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    Not that I know if. I planned to have a fitting screw into the hole in the downpipe and use a weak fan to draw the exhaust gasses down that tube and across the O2 sensor. I'd probably need to try different fan speeds to see what gives the best readings.
     
  4. Polock

    Polock Well-Known Member

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    is there a picture or book on the old yamaha O2 tuner someplace?
    i can't see how a sensor could go through a 5mm hole, now it could let exhaust out to go some sort of chamber with a O2 sensor in that
    or
    a temperature probe would fit in the hole and let you tune EGT the same for all cylinders but nobody knows what that temp should be
     
  5. Rooster53

    Rooster53 Well-Known Member Premium Member

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    This link has a photo of the original unit, and maybe the probes laying on top but the resolution makes it hard to see what they are - it appears to measure CO and HC

    https://www.xjbikes.com/forums/threads/exhaust-gas-analyzer-for-tuning-mixture.125471/

    The chamber idea makes sense to me and dkavanah talked about the adapters in the above thread. He mentions using a fan but I don't see why you would need one as you could just rely on exhaust pressure as long as the sensor is upstream far enough to not give a false reading - a storage chamber could make it a bit easier to place the sensor or just adequate length of tubing on the downstream side.

    The other issue is what type of sensor - O2 (narrowband) or A/F (wideband). The wideband would seem like the best choice given that the narrowband tends to indicate either rich or lean because of the steep curve, whereas the wideband sensor can give a direct readout over a larger range, which seems more appropriate to tune an air cooled engine to slightly rich.

    The narrow band is by far the simplest, but I am not sure how you ensure the correct temp on either one or say what happens if they are too hot. I bring that up as normally the O2 sensor (750 degrees nominal) or A/F sensor (1200 degrees nominal) are often equipped with internal heaters that are PWM driven based on engine parameters. My limited knowledge I am guessing a direct 12V to the heater would likely be OK, especially if tuning at idle.
     
  6. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The probes for the Yamaha unit are the same type as shown in the handheld unit I linked earlier. The sensor is onboard the handle of the probe.
    IIRC the Yamaha unit was made by SUN.
    They did only measure CO and HC, as that was all that was required at the time. The newer handleld units also measure O2 and NOx (I believe that is correct anyway).
     
  7. Minimutly

    Minimutly Well-Known Member

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    Good stuff here - I've used a narrowband lambda on and off (pardon the pun) for years, yes it does switch over right where you want it to have a "slope", but it tells you if your stumble is a rich or weak one. Heater wise just put a 12V supply on it. The wideband is a different kettle of fish altogether, it uses an oxygen "pump" cell to offset the reading, so allowing itself to use oxygen as the read medium - very clever 20 yrs ago, and expensive at the time. Now they are relatively cheap. They do "go off" if they overheat, and I read somewhere (here?) recently that pressure can affect them.
    If you common all your headers together, make sure you have enough downstream pipework to prevent negative pulses drawing ambient air in and slewing your readings.
     
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  8. Dave in Ireland

    Dave in Ireland Well-Known Member

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    I have a wideband sensor on the GS and it's been a major step forward in finally settling the jetting for that bike.
    Then again, I'm only tuning one carb...
     
  9. MrSeca

    MrSeca Active Member

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    Would anybody know how to hook this darn thing up? The instructions are generic and are just not helpful. I'm completely confused.
     

    Attached Files:

  10. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Looks like this would work as colors match for universal O2 sensor. They really should have included this diagram.

    upload_2020-11-18_15-55-59.png

    You can verify heater as white to white should be about 4 to 8 ohms

    The instructions you posted have the Air/Fuel Ratio Gauge setup fairly clearly, just use the O2 black wire to gauge green for signal.
     
  11. DaygloDavid

    DaygloDavid Active Member

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    My 1980 (UK) XJ650 has what I believe are OEM header pipes from an American Seca model which have the 6mm dia. bosses welded on for exhaust gas analysis. A friend got a 6mm dia. bolt, drilled a hole in it and welded a compression fitting to it. I length of coiled copper tube was then attached to the fitting. This set up was used in conjunction with the exhaust gas analyser on a dyno machine to check the O2 content at idle. The bike was only idling on three cylinders, #3 cyclinder wasn't getting hot. At idle, the pilot air screws were adjusted to set the carbs. up properly.

    This video shows the carbs. being balanced after setting up the air/fuel ratios,
     
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  12. MrSeca

    MrSeca Active Member

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    Thanks for bringing another step closer. Could you actually tell me how to hook it up? It's still a little unclear for me. For example, according to your diagram it says the two white wires go to "heater", what does that mean? What heater do I hook it up to? Do I even have to connect those? This is still all very confusing.
     
  13. jayrodoh

    jayrodoh YimYam Premium Member

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    Red and yellow from the gauge to 12V+.
    Sensor gray and black from gauge to ground/negative.
    Sensor black to green from gauge.

    The white wires from the sensor also need 12V+ and ground for the heater. The heater is used to bring the sensor up to operating temperature quickly and ensure it stays hot enough for an accurate reading.
     
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  14. MrSeca

    MrSeca Active Member

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    THANK YOU!!!!! OMG! So I can put the two white wires on the + side of the battery?
     
  15. jayrodoh

    jayrodoh YimYam Premium Member

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    Sorry, one white to positive and one white to negative.
     
  16. MrSeca

    MrSeca Active Member

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    Just hooked it up and everything turns on! I'll throw the sensor into the tail pipe and see what happens but ultimately I want to find some "sacrificial headers so I can drill holes for the sensor to fit into.
     
  17. Minimutly

    Minimutly Well-Known Member

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    Unlikely it will work in the tailpipe, the pulses from the exhaust will draw air back in. You should really drill the collector and live with not knowing which is rich/lean.
     
  18. XJ550H

    XJ550H Well-Known Member Premium Member

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  19. XJ550H

    XJ550H Well-Known Member Premium Member

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  20. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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