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Thread: New member - F650 warm starting issue

  1. #21
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    On your F650, the carburation the engine gets is the sum of that provided by the two carbs fitted to your bike. If one carb idle mixture is lean and the other is correct then the idle mixture the engine gets will not be as weak as it would have been with just one carb fitted - basically, your engine is likely to get the average of the two settings. I would set the weak idle mixture to be the same as the other one but you'll then need to adjust both by the same amount to find the optimum set up for your engine.
    2006 F650GS in Black
    9,300 Miles

  2. #22
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    F650 1997
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    Apr 2020
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    Bregenz, Austria
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    Quote Originally Posted by AWJDThumper View Post
    I would set the weak idle mixture to be the same as the other one but you'll then need to adjust both by the same amount to find the optimum set up for your engine.
    thanks for the quick response, i want to make completely sure I understand.
    As I can only access the idle screw on the right-hand carb, which was set to lean, I am assuming that the other carb is also set the same, therefore also too lean. As I cant gain access to the left hand carb idle screw at the moment, I would like to adjust the right hand to the correct factory settings, and set the other one the same when my special tool arrives. This will mean a week of riding with differing carb settings, one correct and the other lean. From what I read from you post, this is not the BEST setup (theoretically they should be the same), but is not detrimental and is an improvement over both carbs being set too lean. Correct?

  3. #23
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    Yes. Basically, if both were set too lean then adjusting one will make things better. Presumably, there's not enough room under the carb to allow you to use a short slotted screwdriver?
    2006 F650GS in Black
    9,300 Miles

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  5. #24
    Bike
    F650 1997
    Join Date
    Apr 2020
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    Bregenz, Austria
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    Adjustment tool arrived, allowing me easy access to both the idle mixture setting screws. Screwing them all the way in required 2 turns, in my opinion, considering the stock setting is 4.5 turns out, too lean. I have now set them to 3 turns out and the bike is running fine, idle is stable, and I noticed an improvement to the warm starting issue. Now my only issue is the idle speed. When warm, the bike idels at just over 1500 rpm. I cant reduce the speed using the adjustment "knob". I can increase the speed so I know the knob is working, however screwing back out, I cant get the idle speed any lower than just over 1500 rpm. All cables seem to be working fine. What could be the issue here and what can be checked (and how), without disassembling half the bike to get at the carb?

    many thanks

  6. #25
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    On this type of carb, I believe closed butterfly valves should cut off the fuel air mix to the engine and effectively stop it. I would therefore check that with the knurled knob fully wound out to give min idle speed that the butterfly valve spindle appears to be rotated as far as it could possibly go and is not being limited by the idle speed adjuster or its bracket?
    2006 F650GS in Black
    9,300 Miles


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