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Xj750 balking at 7000rpm

Discussion in 'XJ Technical Chat' started by Johnius, Sep 30, 2017.

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  1. Johnius

    Johnius Member

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    1981 XJ750R runs pretty awesome when below 7000RPM and when quickly accelerated through that range. Slow throttle increase to 7000 reveals a "running out of fuel" feel to the engine. Very noticable at 80mph+, moderately so keeping it in first or second gear. Carbs rebuilt by Hogfiddles, synced by myself. Intake mod: K&N air filter. Exhaust mod: MAC 4-into-2.
     
    Johnius, Sep 30, 2017
    #1
  2. k-moe

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

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    Problem identified.
    Get an EMGO, or OEM, paper filter.
     
    k-moe, Sep 30, 2017
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  3. Johnius

    Johnius Member

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    It's in the mail. Thanks, @kmoe! I knew I could count on the experts here!
     
    Johnius, Sep 30, 2017
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  4. Jetfixer

    Jetfixer Well-Known Member

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    ^^^^+1 kmoe is da man ...when I got my seca it had a k&n filter it ran like crap put paper filter in problem solved . When you would run it wide open fell on it's face now that I sorted out carbs this thing flat out growls .
     
    Jetfixer, Sep 30, 2017
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  5. Johnius

    Johnius Member

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    So, I had a rough year riding-wise and finally /installed/ the paper filter and put winter pul in it. Haven't gotten it to full throttle yet, but I can tell I'm going to need to retune it for the paper filter. 29 degrees F this morning and she was idling no choke.
     
    Johnius, Dec 10, 2018
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  6. Toomanybikes

    Toomanybikes Well-Known Member

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    How far up from stock size on jets did you go?
     
    Toomanybikes, Dec 10, 2018
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  7. Johnius

    Johnius Member

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    Stock jets. But I tuned with the K&N installed.
     
    Johnius, Dec 10, 2018
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  8. Toomanybikes

    Toomanybikes Well-Known Member

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    Any bike I have tuned ( dozens) for 4-2 or 4-1 non oem exhaust has needed more fuel at higher rpm. One sometimes 2 sizes up from stock.
     
    Toomanybikes, Dec 11, 2018
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  9. Colin 85 700

    Colin 85 700 Active Member

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    And if it requires more fuel... It makes more horsepower! Oh Ho Ho... Horsepower!
     
    Colin 85 700, Dec 12, 2018
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