Two Seconds To Return To Idle

Discussion in 'Bonneville' started by bruno_c, Dec 1, 2022.

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  1. Tom Swift

    Tom Swift Active Member

    Sep 24, 2021
    I think fuel gets cut only while in gear with the clutch out. In neutral or with clutch in, it should be in closed-loop mode so blipping the throttle would be running a straight stoichiometric mixture only.
    • Agree Agree x 1
  2. nickjaxe

    nickjaxe Active Member

    Sep 2, 2020
    Cheshire UK
    Good point yes.
    • Agree Agree x 1
  3. Baza

    Baza Elite Member

    Jul 25, 2020
    Home of Amazing Grace
    Very esoteric.
    • Agree Agree x 2
  4. Tom Swift

    Tom Swift Active Member

    Sep 24, 2021
    Closed-loop mode is when only the O2 sensor determines correct AFR for most complete burn under low load conditions. It kicks in at idle, slow speeds, cruise and anytime the clutch is pulled in or transmission is in neutral.

    Open-loop mode is when the all the other sensors along with the ECU's programmed fuel maps and ignition curves take control to add the necessary amount of fuel for making power whenever the throttle is increased.

    Fuel-cut mode shuts the fuel off when coasting in gear with the clutch lever out and throttle released or decreased sufficiently.
    • Agree Agree x 1
  5. Baza

    Baza Elite Member

    Jul 25, 2020
    Home of Amazing Grace
    Thank you for the above explanation, but my comment related to your use of the term “stoichiometric”, I very much doubt there many chemists on here.

    For the benefit of others I assume the initialism AFR is air/fuel ratio?
    • Useful Useful x 1
  6. Eldon

    Eldon Elite Member

    Nov 14, 2018
    North Yorkshire
    Yes to AFR ;)

    And stoichiometric is a theoretical value (around 14 parts air to 1 part fuel) to aim for going back to the olden days for most efficient burn. Now with lean burn technology I would expect all manufacturers to be well shy of this with the emission laws prevailing.
    • Useful Useful x 1
  7. MEM62

    MEM62 Well-Known Member

    Aug 24, 2020
    Basingstoke, Hampshire
    The RPM on mine is slow to fall after closing the throttle too. This is in stark contrast to my GSF1250 and my wife's MT07 where the drop is almost instant.
    • Useful Useful x 1
    • Agree Agree x 1
  8. Solution6

    Solution6 New Member

    Oct 13, 2023
    Richmond, UK
    Any luck with this?

    Same thing with mine. Changed the throttle handle, cleaned throttle body, changed spark plugs, issue still here.

    2017 ST 15K miles. But has been doing this since I picked her up at 4K.
    • Agree Agree x 1
  9. Jet City

    Jet City Noble Member

    Sep 24, 2018
    Seattle, Washington USA
    My 2018 Bonneville T120 has always done this.

    No big deal, it’s just not like any other bike I’ve owned.
    • Agree Agree x 1
  10. Kinjane

    Kinjane Active Member

    Oct 15, 2017
    Bristol, Land of Enger
    Just because it’s always done it, it doesn’t necessarily make it right! Could be a very easy fix.
    Have you checked or had you dealer check the TPS sensor output voltage?
    I’ve fixed several T120 triumphs where this problem has been caused by low output voltage.
    It takes less than 5 minutes to access the TPS unit, adjust it to spec and button up
    the left hand ‘float bowl’ afterwards.
    • Like Like x 1
    • Agree Agree x 1
  11. bruno_c

    bruno_c New Member

    Oct 19, 2018
    This is interesting.
    Kinjane, could you explain how to check and adjust the tps unit, or where to find a tutorial.
    • Agree Agree x 1
  12. joe mc donald

    Dec 26, 2014
    slough / burnham
    Peeps i think everyone is looking for faults that really isn't there. My 660 fires up at over 2000 revs. I give it a ride and every thing drops nicely. It has a slow response at tick over. But then the earlier Bonnies have cables and are sprung helping the shut of when twitching the throttle. Just my twopence.

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