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650 seca turbo carb (mikuni?) on NA 650 seca

Discussion in 'XJ Technical Chat' started by amcon17, Jun 26, 2021.

  1. amcon17

    amcon17 New Member

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    I’ve searched for a thread relating to this but haven’t found one so I hope I’m not duplicating a question.

    A good friend of mine bought a 650 seca and had the carburetor stolen from it so he ent on eBay and unknowingly bought a replacement for the seca turbo.

    I have a 650 maxim so I’m moderately familiar with the carb but this turbo version is entirely different. Threw the turbo carb on his bike and turned it over only to have it pinned at 7 or 8k rpms until we killed the power.

    In short my questions are:
    1. Is there an obvious reason that I’ve missed as to why it would cause the bike to scream at high rpms with no throttle input simply because the carb is tuned for turbo?

    2. Is there any reason we couldn’t tune the carb to run well without boost?

    Thanks in advance guys
     
  2. Simmy

    Simmy Well-Known Member

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    There is a difference in the throttle cables between what is required for the Mikunis you have in place now. Disconnect the throttle cable for now to verify it’s not holding it open.
    You can pull the metal end from the sheathing and trim the sheathing about 1/2 an inch.
    Then fit the metal cap back.
    Obviously the proper route is to get the Hitachi carb rack back in place as what you have is not going to be ideal. Will the jetting be lean without boost pressure?
    Try trading with @hogfiddles he might be open to that, the Turbo rack are a more rare and valuable set.
     
    Last edited: Jun 26, 2021
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  3. Fuller56

    Fuller56 Well-Known Member

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    And the Turbo carbs have a small, about 1.5 inch, cable between their attachment point and the throttle cable from the hand grip. It is easily lost and if you do not have that it is likely the carbs were held wide open when you started the bike.
     
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  4. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    And the turbo carbs are jetted differently. And unless the carbs came with a guarentee you don't know if they are even set up correctly or don't have any vacuum leaks.
    Really it's better to get the correct rack of Hitachis and sell the Turbo set.
     
  5. Minimutly

    Minimutly Well-Known Member

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    1. The turbo carbs are no different in the throttle design - so you have them set wrong. Need to bench synch and set them just off closed.
    2. No, there is no reason - I would suggest going to the Fj600 settings - I have a set of these on my 650 and can't find any issues with the jetting.
    3. If you don't want to be faffing about with jets go with @kmoe's advice.
     
  6. Minimutly

    Minimutly Well-Known Member

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    No, don't be silly, they would be closed, and realistically, surely not having the return springs pulling on the throttle would be obvious?
     
  7. amcon17

    amcon17 New Member

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    Appreciate the help guys. That 1.5 inch cable was there, I made sure there was some slack in the line too.

    No worries though, he found the right carb and is just gonna sell this one.

    thanks again
     

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