Air Fuel Ratio/Lambda for Evo

Discussion in 'Softail Models' started by Piotra, May 23, 2011.

  1. Piotra

    Piotra Active Member

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    Hello
    I'm planning to tune the carburetor. I can go to the car shop and use a gas analyzer. It shows lambda value. Of course when I ask a guy in the shop, he said that lambda should be 1. Looking at this table it of course mean that AFR should be 14.7. But when I’m reading forum I know that AFR should be less (rich mixture). So the question is what lambda should I obtain during tuning.
    There is nice table for conversion AFR to lambda:
    http://www.tatech.fi/cms/uploads/Lambda_vs_AFR.pdf

    My bike has RevTech 100 inches Evo style engine, Mikuni HSR 42 carb, single fire ignition with dual plug heads. I have straight drag pipes. When I’m reading posts there is a lot of different information that the best (and most safe) is AFR about13.2-13.8 (the range is from 12.5 up to 14). It’s mean that lambda should not be 1 but less about 0.90-0.94. But let me know what value should I set. I prefer value that will be safe for engine, to not go to hot.

    And question what to do before tuning. Run few miles of course. What temperature of oil should I have before tuning and how many RPM should I have during tuning? Should I set about 1000 RPM? During tuning what values AFR/lambda should I have on idle and what values should I have on for example 2000 RPM?

    Sorry for a lot of questions but I want to do it correctly and there is a lot of different values AFR and I think mostly for TwinCams not carburetor.

    Best regards, Piotr

    PS. Maybe you can also give me other values like CO, CO2, HCH ......
     
  2. Hoople

    Hoople Account Removed

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    If I was using pure gasoline (which is your supplied chart), I would run,

    Idle Lambda (no load) .90 - .91
    Mid range cruise Lambda (under steady load) .94 - .95
    Wide open throttle Lambda (under heavy max load) .83 - .84

    I am not saying these numbers are right for everyone but they are what I shoot for.
    For a carb bike, it is much harder to select what you want and most times you will settle.

    The other readings:

    CO is another way to look at how rich or lean the engine is running. The higher the CO, the more rich the mixture is. Very useful reading. But only useful for tuning if read before the catalytic converter.

    CO2 can be disregarded in this case since you do not have a catalytic converter on the bike. The cat adds an oxygen molecule to the CO and forms CO2. Can be used for measuring cat efficiency.

    HC is a measure of how well the engine is using the fuel your putting into it. HC is unburned fuel coming out the pipe. There will always be some. The lower the number the better. If above 250 PPM look at the quality of the spark, timing, compression etc.

    Remember that:
    Lambda of 1 for pure gasoline is 14.7
    Lambda of 1 for E10 is 14.4
     
  3. bc45

    bc45 Active Member

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    In therory stoichiometry is when rhe mixture has hust just enough oxygen to completely burn the avalible fuel. which burnes really hot.

    Lamda is the ratio of actual air fuel ratio to stoickiomety for a given mixture,
    Lamda 1 represents a stoich mixture.
    Taht is my understanding of Lamda and stoichiometry.

    I dont know what mixyou need for your combo but you would probly be in the .9-- somethings of lamda.
     
  4. Piotra

    Piotra Active Member

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    We have here two types of gasoline Eurosuper 95 and Superplus 98 so I think that this is more pure gasoline than E10 (with 10% of ethanol, Am I right?)
     
  5. Hoople

    Hoople Account Removed

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    Good question, I really don't know. I just mentioned the E10 fuel just in case since I don't know the rules outside of the U.S.