T140v Rough Running - Left Side Missing

Discussion in 'Triumph General Discussion' started by MartinUK, Nov 16, 2025 at 3:33 PM.

  1. MartinUK

    MartinUK New Member

    Sunday
    2
    3
    UK
    I've just got a 76 T140V. The previous owner said he had refurbed the carbs but on the ride home it was missing and would not rev smoothly. Today at home I could only start it using easy start. Once warm the left side is missing and rough running together with some blue/grey smoke out of the exhaust. I swapped the plug leads and it's still the left side that is rough. I can also see that smoke is leaking out of the front of the left cylinder, where the exhaust goes in, not much and only really evident when I try to rev it. So, is this a carb issue?
    If I put a new plug in the left side it will run OK for a few minutes but then starts the problem again. If I take out that plug it is wet. The bike has wassell electronic ignition. The carbs are the Amal type with a tickler but also have a choke slider with a lever on the left side.
     
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  2. TRIPLE X

    TRIPLE X Senior Member

    Sep 1, 2021
    665
    243
    Norfolk
    It might be worth swapping the coils over to rule out a defective coil on the left side?
     
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  3. MartinUK

    MartinUK New Member

    Sunday
    2
    3
    UK
    Thanks, gonna try that but I've already swapped the plug leads so that also means all the circuit up to there swaps too(including coils).
     
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  4. Romeo Keller

    Romeo Keller New Member

    Oct 18, 2025
    0
    1
    Switzerland
    I think this is an oil-problem. Pistonrings or valveguides worn. So you have to strip the cylinderhead and find the problem. Regards from Switzerland
     
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  5. TRIPLE X

    TRIPLE X Senior Member

    Sep 1, 2021
    665
    243
    Norfolk
    Yes, it does appear to be burning oil hence the blue smoke. Might be worth doing a compression test before stripping it down to see if there is a significant difference between cylinders.
     
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  6. Mike_Oxmall

    Mike_Oxmall New Member

    Jun 18, 2025
    19
    3
    Nr Scunthorpe
    #6 Mike_Oxmall, Nov 17, 2025 at 5:23 PM
    Last edited: Nov 17, 2025 at 6:54 PM
    Is the choke opening on the left carb. I never had choke sliders in on my 120V.

    Take the choke sliders out. You don't need them. Just a good tickle and she should start perfectly.

    Are the slow running jets set at 1 1/4 -1 1/2 turns out.

    I had a "Gunson" colour tune years ago and you could set the slow running perfect with it.

    Is the left needle in the correct position height wise.

    Worst case. . . swap the carbs over and see what she runs like.

    Inlet manifold may be cracked or bad gasket.
     
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  7. TRIPLE X

    TRIPLE X Senior Member

    Sep 1, 2021
    665
    243
    Norfolk
    If it has electronic ignition the condensers should have been ditched?
     
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  8. Mike_Oxmall

    Mike_Oxmall New Member

    Jun 18, 2025
    19
    3
    Nr Scunthorpe

    Correct. I'm doing 3 things at once and just ran through my thoughts forgetting he had EI fitted.

    So we're back to carbs. Inlet manifold may be cracked or bad gasket.
     
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  9. Iceman

    Iceman Crème de la Crème

    Apr 19, 2020
    2,748
    1,000
    Lancashire
    I would undertake a compression test first, however, given that you say it emits blue/grey smoke it is a strong indication of burning oil. It will need the head and barrels removing to inspect. Don't run it anymore, if a ring is broken it can cause further damage.
     
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