DT125r Problem between 4000-5000rpm

Discussion in 'Motorcycle Technical Discussion' started by Greg, Jun 24, 2005.

  1. Greg

    Greg Guest

    Ive got an 89 dtr125 (with ypvs servo kit) which runs a bit rough
    between 4k and 5k, seems like a missfire or like its not burning the
    fuel correctly.
    Ive fully stripped and cleaned the carb and its at factory settings,
    reeds are in good shape, doesnt seem to be any leaks from the L/H crank
    seal, the bike has a new piston and top end gasket set, just tried
    another ignition coil today from another bike but no difference, tried
    a cdi unit from a tzr125 but no luck, no play in crank bearings or big
    end/small end. Plug runs brown in the middle with black round the
    edges.
    In the rest of the rev range the bike feels fine and goes like a
    rocket.
    I'm just about beat with this one and would much appreciate any
    suggestions.

    P.S. Does anyone know what the pipe is for at the back of the carb,
    below the venturi (mikuni flatslide) It doesnt seem to be a breather as
    it looks to be part of the main jet circuit, should this pipe connect
    to somwhere els on the carb?


    Cheers
    Greg
     
    Greg, Jun 24, 2005
    #1
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  2. Was the DT-125R ever sold in the USA? Do you know a link to an on-line
    parts fiche for your machine? I looked at www.partsfish.com and your
    motorbike isn't listed there...

    I suppose the pipe you describe is a brass tube. Some carbs have such a
    tube and it sucks fuel directly out of the float bowl into the venturi
    at high engine RPM...

    OTOH, I've also seen straight brass tubes about an inch long that were
    part of the idle circuit. They would extend down from the carb body
    into a well in the float bowl. The well would fill up with gasoline and
    the idle jet would suck gas out of this well. The apparent purpose for
    that seemed to have been to reduce emissions at low throttle settings
    when fuel splashing around in the float bowl would constantly change
    the fuel/air mixture. The idle jets in that type of carb (Mikuni SS CV
    carbs) were hidden above rubber plugs and they didn't extend into the
    float bowl at all...
     
    krusty kritter, Jun 24, 2005
    #2
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  3. Greg

    Greg Guest

    Its like an overflow hose that comes from underneath the venturi. Ive
    ordered a haynes workshop manual for the bike so hopefully that will
    show what its for.
     
    Greg, Jun 24, 2005
    #3
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