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size matters?

Discussion in 'XJ Technical Chat' started by gmoncrief, Dec 13, 2011.

  1. gmoncrief

    gmoncrief Member

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    I ran up against a strange find while swapping Seca 750 motors. The core motor that I scavenged the manifolds from is a 748cc and the manifolds where mounted on them. I’m stating this because I don’t know any of the history of this particular motor, bought it as a core for parts. Anyway when I went to install the carbs they didn’t fit!!!! The bolt pattern is the same and they bolt up to the head, but the diameter is about 2mm smaller then my original manifolds. So I’m guessing that the prior owner of this motor intentionally or accidentally installed XJ650 maxim/seca manifolds??? Can anyone confirm that the XJ650’s (non-turbo) manifolds look very similar to the 750’s but are not inter-changeable?
     
    gmoncrief, Dec 13, 2011
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  2. iwingameover

    iwingameover Active Member

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    Chacal would know for sure. I think the nonturbo 650/750 motors take the same carbs just different jets.
     
    iwingameover, Dec 13, 2011
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  3. cutlass79500

    cutlass79500 Well-Known Member

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    I agree same carbs different internals.

    Are you sure they did not shrink and get hard from sitting. Someone could have swapped carbs and manifolds off another bike also. I remember schooter putting non cv carbson his 750 off a sohc honda 750
     
    cutlass79500, Dec 13, 2011
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  4. tskaz

    tskaz Active Member

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    All 650 non-turbo and 750 motors used the same 32mm Hitachi carbs.

    The non-YICS and YICS 650 motors did use different engine-to-carb boots, not sure if the 750 mounts were interchangeable with either of these two motors though.

    I agree with IWGO, PM chacal and you will have the definitive answer shortly.

    Let us know what he says so we can improve our XJ knowledge?
     
    tskaz, Dec 13, 2011
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  5. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    It's not the carbs; it's probably the manifolds like you said.

    YICS motors and non-YICS motors had differently angled intake manifolds. Differently angled and differently MOUNTED; one type motor has a mounting bolt pattern like / / / / and the other is / / \ \ but I don't remember which is which. (And I don't feel like poking about in the garage right now.)

    Early "normally aspirated" (non-turbo) 650s were not YICS motors. The '80 and '81 Maxim 650 and '82 Seca 650 all had non-YICS motors.

    All of the 750s were YICS motors. Before you drive yourself too crazy, either look up the shorty VIN or check the front of the cylinder casting and be sure you have two 750 motors there.

    Another possibility is that you've got a 750 Seca and 750 Maxim motor there; depending on the year, the Max motor may have different specs. I'm not sure, this is a "chacal question." It's out of my pay grade.

    Is that at least part of the answer you needed?
     
    bigfitz52, Dec 13, 2011
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