Funduro won't rev (again)

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Thread: Funduro won't rev (again)

  1. #1
    Bike
    F650 Funduro 1994
    Join Date
    Jul 2020
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    Poole
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    Default Funduro won't rev (again)

    This is a well rehearsed issue it seems, The bike doesn't start easily, will only run on choke initially, once it's running it will idle OK without choke when warm, and will rev to about 4k if I'm gentle with the throttle. If I open the throttle quickly it farts and dies. My first ride was cut short as the bike won't go up hills, and is embarrassingly, dangerously slow.

    I've tried the following:-

    Cleaned tank, filter, new fuel hose, rebuilt carbs (rebuild kit OEM labelled SKU05105-UK BMW F650 Mikuni BST33 GS500E). Carbs good, fuel good, fuel flow good, fuel level in carbs good. There is no water in the fuel.

    New plugs NGK D8EA, silicon leads and correct 5K NGK caps.

    New battery measures 12.7v, turns the bike over well. Voltage regulator in GWO, goes to mid 14v, tried a new one as well, gives exactly the same result.

    Intake manifold removed and checked, it's fine, no leaks.

    Given that the choke does make a difference, I'm thinking air leak, apart from the inlet manifold though I can't see where that might be.

    The needles which came with the carb kit were considerable shorter than the ones I took out, so I've put the old ones back in, makes no difference.

    I wonder whether the jets are wrong in the carb kit, and if so would it make such a huge difference, and how do I check? Anybody out there had issues with carb kits?

  2. #2
    Bike
    02 dakar
    Join Date
    Dec 2019
    Location
    Scarborough
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    Default

    Thinking not about revs but where throttle is i.e . 3rd open etc might help diagnose if it's pilot jet or main jet causing issues. Coil good, not breaking down under load ? Does restricting air to carb make it better, indicating running weak. Local bike shop starts at £250 to look at carbs, getting to be specialist now that people are used to laptops telling them what to do. ! Dyno with fuel ratio measure would sort it

  3. #3
    Bike
    F650 Funduro 1994
    Join Date
    Jul 2020
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    Poole
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    Default

    Jets seem logical, good idea! I will take the carbs out again today and have a look. Cheers!

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  5. #4
    Bike
    02 dakar
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    Dec 2019
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    Default

    In the labeling for the rebuild kit, says sku aND gs500e it's not for a suzuki gs500e is it. They use the same carb as bmw but different jet sizes, mains suzuki 130, bmw135 I think . might explain why needles shorter.

  6. #5
    Bike
    F650 Funduro 1994
    Join Date
    Jul 2020
    Location
    Poole
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    Default Sorted

    The replacement main jets were much smaller than the old ones, put the old jets back in, now all good! Good steer mate, thanks!

  7. #6
    Bike
    02 dakar
    Join Date
    Dec 2019
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    Scarborough
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    Default

    Glad your sorted, one of those frustrating jobs. You on the right track in your first post


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