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Thread: Low AFV - seems to be after short ride after reset

  1. #1
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    Wink Low AFV - seems to be after short ride after reset

    I fairly recently acquired a 2008 XB12R from my dad - my 2nd Buell I've had. Since I acquired it from him, it stalled at startup, and didn't have any power on accleration beyond 1/3 throttle. My dad chalked it up to being cold natured - he's a Harley guy, never rode it hard at all. I used my Buelltooth earlier today, found the AFV was at 77%. Reset AFV, took on a short ride, value did not change and performance was back! Any possible issues I should be keeping an eye out for?

    Was considering looking into the RevMoto "race" tune for stock bike. Don't know if anyone has used it, what kind of luck / power increases anyone has had. I likely will in a few months get the RevMoto exhaust as well. Don't know what, if anything, RevMoto charges for their maps as well. I know, a lot of questions in one post.. Anyone have any input? Thanks in advance!

  2. #2
    Senior Member 34nineteen's Avatar
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    Quote Originally Posted by TekratFL View Post
    I fairly recently acquired a 2008 XB12R from my dad - my 2nd Buell I've had. Since I acquired it from him, it stalled at startup, and didn't have any power on accleration beyond 1/3 throttle. My dad chalked it up to being cold natured - he's a Harley guy, never rode it hard at all. I used my Buelltooth earlier today, found the AFV was at 77%. Reset AFV, took on a short ride, value did not change and performance was back! Any possible issues I should be keeping an eye out for?

    AFV of 77% is an indicator of running very rich.

  3. #3
    Senior Member Barrett's Avatar
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    NO mention of mods if any....mileage....and value used for AFV "reset".
    Your ECM is receiving values it doesn't like and interpreting same as either loss of air flow or unnecessary additional fuel being presented. In essence, it believes there's too much fuel present during combustion, therefore reducing injector pulse width. Hence the 77% AFV you saw. Assumptions are worthless but if reset to 100 and remained there for time-being, bank on it dramatically dropping in near term. Dicking with tunes, mufflers and other assorted goodies will exacerbate the problem and loss of base-line. My experience dictates that 1 or more of the below causes this situation and therefor, all should be checked. Have seen 2008-2010 models receiving an incorrectly performed manual TPS throttle synch by ham-fisted owner causing this precise problem.


    1-IEV valve inoperable
    2-Collapsed muffler internals
    3-IEV system inoperative and stuck in closed position
    4-Historical FC's stored and should be examined for clues
    5-Restricted/collapsed air filter
    6-Airbox base plate to TB connector boot misaligned or pinched
    7-Failing O2 sensor
    8-One or both injectors failing
    9-TPS inadvertently reset via "throttle synch" method and done incorrectly.

  4. #4
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    Wink

    Quote Originally Posted by Barrett View Post
    NO mention of mods if any....mileage....and value used for AFV "reset".
    Your ECM is receiving values it doesn't like and interpreting same as either loss of air flow or unnecessary additional fuel being presented. In essence, it believes there's too much fuel present during combustion, therefore reducing injector pulse width. Hence the 77% AFV you saw. Assumptions are worthless but if reset to 100 and remained there for time-being, bank on it dramatically dropping in near term. Dicking with tunes, mufflers and other assorted goodies will exacerbate the problem and loss of base-line. My experience dictates that 1 or more of the below causes this situation and therefor, all should be checked. Have seen 2008-2010 models receiving an incorrectly performed manual TPS throttle synch by ham-fisted owner causing this precise problem.


    1-IEV valve inoperable
    2-Collapsed muffler internals
    3-IEV system inoperative and stuck in closed position
    4-Historical FC's stored and should be examined for clues
    5-Restricted/collapsed air filter
    6-Airbox base plate to TB connector boot misaligned or pinched
    7-Failing O2 sensor
    8-One or both injectors failing
    9-TPS inadvertently reset via "throttle synch" method and done incorrectly.
    Bike is bone stock - still even has the stock air filter. Mileage is just a hair under 8100 miles. Only change that I have done is fresh fuel and new spark plugs. AFV I set to 100. I know the boot is installed properly - issue occured prior to replacing spark plugs, and made sure to place boot back properly. I also did TPS reset, did not appear to make any difference. No codes in system. I guess I'll have to dig deeper into O2 or exhaust issue. I know most aftermarket exhaust essentially bypass the IEV. The reason I'm leaning away from injectors, is that once I set AFV to 100, it ran like it should.

  5. #5
    Senior Member 34nineteen's Avatar
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    Quote Originally Posted by TekratFL View Post
    Bike is bone stock - still even has the stock air filter. Mileage is just a hair under 8100 miles. Only change that I have done is fresh fuel and new spark plugs. AFV I set to 100. I know the boot is installed properly - issue occured prior to replacing spark plugs, and made sure to place boot back properly. I also did TPS reset, did not appear to make any difference. No codes in system. I guess I'll have to dig deeper into O2 or exhaust issue. I know most aftermarket exhaust essentially bypass the IEV. The reason I'm leaning away from injectors, is that once I set AFV to 100, it ran like it should.
    Unless you have a leaking injector.



    The exhaust valve in the muffler isnt going to cause this. Not all XB's had one, neither did the factory race muffler.


    Last edited by 34nineteen; 05-25-2022 at 11:05 PM.

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