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Throttle blip to bring idle down?

Discussion in 'XJ Technical Chat' started by Stumplifter, Jun 9, 2015.

  1. Stumplifter

    Stumplifter Well-Known Member

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    Vacuum synched my carbs today - interesting to find that 1&2 were out from each other and also out from 3&4 (synched them last spring).

    Noted that the Carbtune directions recommend every 5,000 miles to verify settings - Is it normal for the synch to 'walk out' of spec like that?


    Anyhow - after the synch went for a ride and marveled at how smooth and snappy things were. Also noted that when stopping that idle was at around 1,700 - a blip of the throttle will bring it down to 1,100.

    What up with that?
     
    Stumplifter, Jun 9, 2015
    #1
  2. k-moe

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

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    Your idle mixture is lean.
     
    k-moe, Jun 9, 2015
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  3. Stumplifter

    Stumplifter Well-Known Member

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    I will grab my colortune plug and recheck . . . .
     
    Stumplifter, Jun 9, 2015
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  4. k-moe

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

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    That or you have an undiscovered vacuum leak.
     
    k-moe, Jun 9, 2015
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  5. Polock

    Polock Well-Known Member

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    put some silicone in the throttle tube and some oil in the cable, see how it works then
     
    Polock, Jun 9, 2015
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  6. Stumplifter

    Stumplifter Well-Known Member

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    Went through with propane tank after putting vacuum caps back on post vacuum synch; even waved it around the boots and seals.

    Lubed throttle cable about a month ago.

    Going to colortune and then re-do the vacuum synch (that is protocol correct?)
     
    Stumplifter, Jun 9, 2015
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  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    yes color tune sync color tune sync....
     
    XJ550H, Jun 9, 2015
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  8. k-moe

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

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    Color tune, synch, colortune, done. The last mixture adjustment will be very slight if at all.
     
    k-moe, Jun 10, 2015
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  9. Polock

    Polock Well-Known Member

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    Open the throttle, close it slowly, reach in and see if you can close the linkage farther with your finger.
     
    Polock, Jun 10, 2015
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  10. Stumplifter

    Stumplifter Well-Known Member

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    Throttle cable was new last year (and re-lubed this year, w/ bacon grease ;))- are you suggesting it is frayed?

    But to answer your question - the cable slackens above the carbs - but if I press firmly on the linkage (near #4) it will slow the idle ever so little and then when I release it comes back up (less than 100RPM deviation). Ass-u-me that this is normal 'play' in linkage and my firm press is showing the slight RPM deviation.
     
    Stumplifter, Jun 10, 2015
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  11. Polock

    Polock Well-Known Member

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    a vacuum leak would come right back up since the leak would still be there. A frayed or sticky cable wouldn't get slack. I think your right about play in the linkage. I had something like that once where the carbs were too clean and the sync mechanism didn't want to slide on the tabs on the carbs, a slow release raised the idle and threw the sync off but a snap fixed the idle and sync, a drop of LPS fixed that. If you have strange things happen while doing the sync, check that.
     
    Polock, Jun 10, 2015
    #11
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  12. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    As the valve clearances change, the sync will change. That's part of why we do carb clinics each year-- to adjust for those changes that may occur in between shim clearance checks. That way we can keep things running as smoothly as possible :)
     
    hogfiddles, Jun 10, 2015
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  13. Stumplifter

    Stumplifter Well-Known Member

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    Duh - that makes sense. I did have to swap a shim this spring, which would explain the synch difference.

    Polock, I actually did have a heck of a time getting 1&2 to synch up with 3&4. Never considered that the witness marks in the synch tabs could be hanging up.
     
    Stumplifter, Jun 11, 2015
    #13

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