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AFR meters anyone?

Discussion in 'Norton Commando Motorcycles (Classic)' started by SteveBorland, Aug 19, 2019.

  1. SteveBorland


    Nov 15, 2010
    After my recent piston experiences, I've been thinking of using an air-fuel meter to remove the guesswork from the carb settings.
    The idea of being able to get an accurate reading of what's happening in the cylinder in real time is very attractive to me, and looking at eBay, most of these meters cost rather less than a set of Jim Schmidt' high compression pistons.

    Has anyone tried this, and are there any recommendations? What I've seen so far is that they all seem to use round gauges, while ideally I would like a smallish rectangular readout.
  2. lcrken

    lcrken VIP MEMBER

    Mar 15, 2009
    I've been using the WEGO III systems from Daytona Sensors for several years now, and recommend them. More info here:


    I have both the single channel and dual channel systems. I've used the single channel system to set up carburetion on a Rotax-powered MZ, as well as my Norton twin landspeed racer. I'm currently using the dual channel unit to set up the fueling on my 2004 961 Norton. Besides displaying the AFR real-time, they have data logging capability. On the 961 I use that to also record both rpm and throttle position along with the AFR. On the other two bikes I just use the AFR, using the real-time display on the MZ, and recorded data on the landspeed Norton. I've had no problems with either system, and have found them very useful.

    This is a picture of the dual channel display installed on my 961.

    Display 1200.jpg

    Last edited: Aug 19, 2019
  3. baz

    baz VIP MEMBER

    May 26, 2010
    I use a cheap Koso narrow band O2 sensor
    You have to weld a bung into one of your down pipes less than 200mm from the head
    The type I have is a small oblong display but it's not illuminated
    I also marked out my throttle drum so that I could tune each phase of the carburetion
    It works quite well but with antique carburettor design it's not perfect
    When you grab a handful of throttle or labour the engine you won't get an accurate reading
    Also don't expect to get it perfect
    But it will tell you which way to go with the main jet / needle position/slide cutaway
  4. pommie john

    pommie john

    Nov 18, 2005
    I use one on my race BMW made by AEM. It cost about $250. You have to weld a bung in your downpipe, but unlike some of the others it's not too fussy where it is as the O2 sensor has its own heater built in. It does draw some current when heating up, but it's been great for setting up carbs.

    The thing you need to know is that although 14.7 is the "ideal" fuel ratio, it's far too weak for normal riding especially on an air cooled bike. The dyno operator I use recommended high 12s on full throttle. A water cooled modern bike can take 13:1 but we need to run a bit richer.
    Yorkie likes this.
  5. SteveA


    Dec 20, 2011
    12.5 to 12.8?
  6. pommie john

    pommie john

    Nov 18, 2005
    Pretty much. 12.5 might be a tad rich, so nearer 12.8.
  7. SteveBorland


    Nov 15, 2010
  8. MexicoMike


    Jan 31, 2010
    FWIW, in my serious engine building days we sometimes adjusted A/F to set up an engine as a rough starting point. But that was all we ever did with that. We then put the vehicle/engine on the dyno and adjusted fueling and ignition timing for maximum power through the rev range. Whatever that turned out to be A/F wise was whatever that turned out to be! It was not unusual for different settings/jets to be used for different cylinders or on either side of multi-barreled carburetors to get the best performance from a particular engine.

    Admittedly, we didn't care about emissions...

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