2004 Bonneville T100 - Curious Problem, Need Your Help!

Discussion in 'Bonneville' started by Fritzl, Sep 16, 2023.

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  1. Fritzl

    Fritzl New Member

    Sep 16, 2023
    0
    1
    Germany
    hey guys,

    my name is Fritz, a litte over 30 years old, enthusiastic about motorcycles, i have quite some bikes from the 70s up to 2000s in my possession. I like to wrench on my own or with friends.

    problem child: Bonneville T100, 2004, 790ccm, 25tkm, at the moment completly orginal with restrictor plate, intake snorkel... carb jetting is also orginal !

    The Triumph was handed over to a Triumph workshop by the previous owner - she no longer wanted to start

    Triumph checked the wiring harness in a comprehensible manner and replaced the crankshaft sensor, control unit, ignition coil and spark plugs with new parts. In addition she got a service.
    Of course that cost a lot of money. After that she started again.

    Now comes the big but: At around 130kmh, it feels like she runs into the limiter ("early"), accelerating above 130kmh is not possible. If you drop the rpm a little you can accelerate up to 130kmh again, that's it. The whole thing is fully replicable. Otherwise it pulls through no dropouts, cut outs, hesitation etc.

    Until now i have done the following:
    crankshaft sensor measured (approx. 600 ohms) - fits
    crankshaft sensor distance checked with feeler gauge (0.85mm) - fits (fully within range/spec)
    side stand switch bridged - no change, error remains
    tps sensor disconnected - no change, error remains
    carburettors disassembled - everything is fine, everything is originally equipped, the float level is correct - no action required
    tank ventilation is also OK. and fuel flow is fine too.
    air filter box (see above) also original with restrictor plate and intake snorkel etc., air filter also great

    I'm currently running out of ideas as to how the error could occur. All components are new (ignition side) and also
    original Triumph parts that match my modelyear. In my opinion, the fuel and air side is also perfectly fine.

    Maybe you guys have an idea? Could the new control unit simply be faulty ? Am I missing something?

    Restrictors of any kind are not installed, i should probably mention that upload_2023-9-16_16-48-45.gif

    Would be awesome if somebody could help !

    Cheers
    Fritz
     
  2. bruno_c

    bruno_c New Member

    Oct 19, 2018
    16
    3
    France
    Did it run fine for some time after ECU was changed?
     
  3. Fritzl

    Fritzl New Member

    Sep 16, 2023
    0
    1
    Germany
    Nope never.
    The previous owner was sure, that it only happend after the repairs.

    EDIT: I added a tachometer (inductive-just wrapped around the sparkwire) in order to check the rpm at which the cutout happens, and its not only 5th gear but also 1-4 incl. neutral !!! The cutout happens always between 4800rpm-5200rpm in every gear.

    regarding restrictors. I even called triumph and asked if there was a igniter (CDI) with a lower rev limiter, but there isnt!

    any ideas ?
     
  4. bruno_c

    bruno_c New Member

    Oct 19, 2018
    16
    3
    France
    It looks like a faulty ECU . I would first check the ECU connector. Then try to swap the ECU.
     
  5. Wattie

    Wattie Well-Known Member

    Feb 25, 2020
    350
    63
    UK
    #5 Wattie, Sep 25, 2023
    Last edited: Sep 25, 2023
    Hi and welcome.
    I've never worked on a Bonnie however the early ones have similar ignition components to my T300 series triumph. The one thing I've read about is that early T100 were sent out with 1.0mm gap on the crankshaft position sensor and a factory bulletin said this should be set to 0.8mm to solve misfire issues. I see you've set yours at 0.85mm, perhaps it's worth dropping the gap? I know the T300's are recommended as 0.8-0.6mm air gap.
    I found a mention to the above in the following thread https://www.triumphrat.net/threads/...rank-position-sensor-nerdy-and-boring.158995/
    Perhaps experienced early bonnie owners could confirm this?
    The other thing I was thinking is perhaps the ignition is earthing somewhere and maybe it would be worth taking the tank off and running the bike in neutral in the dark to see if anything is shorting?
    Good luck.
     
  6. RickM46

    RickM46 Active Member

    Oct 12, 2023
    44
    28
    US
    Fritz, any update?
     
  7. Fritzl

    Fritzl New Member

    Sep 16, 2023
    0
    1
    Germany
    i replaced the brand new orginal triumph ecu with an aftermarket one and the problem was gone !
     
  8. RickM46

    RickM46 Active Member

    Oct 12, 2023
    44
    28
    US
    Wow, never would have thought a faulty OEM ecu to be the culprit; looks like Bruno hit the nail on the head; must have been a bad run of ecus or the wrong one.
     
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