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700 carb sync procedure? And should I colortune before or after?

Discussion in 'XJ Technical Chat' started by quentin, Nov 28, 2015.

  1. quentin

    quentin Member

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    Title is pretty much explanatory. Little background info, I ride an '85 700 airhead. Been having issues with bogging at high RPM (around 7k). I am going to adjust my valves and then (obviously), I plan to make re-sync the carbs. I believe the bike is running lean which is why it bogs at high RPM (I think fuel starvation because if I turn the choke on during WOT runs, it will not bog) - before you ask, no the petcock does not have an issue (I've tried running it on the prime setting and it still bogs), no air leaks in ANY of the carburetor boots, carbs pass the "clunk" test, etc.

    I am planning to colortune the bike to help sort out any air/fuel ratio irregularities. Should I colortune before or after the carb sync?

    And just to clarify for the carb sync: you sync cylinders 1 and 2 together, as well as 3 and 4, and then you sync the left and right "banks" together, right?
     
    quentin, Nov 28, 2015
    #1
  2. k-moe

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

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    Have you cleaned the carbs yet?

    Your diagnosis sounds spot on (being lean at high RPMs), but the cause is going to be something other than a lean idle circuit or carbs being out of synch.

    To the point of your question:

    With the engine at operating temp;

    Colortune the idle circuits.

    Vac sync as you described.

    Colortune again if you really want to (sometimes I do, sometimes I don't).

    also, please keep it on one thread. http://www.xjbikes.com/forums/threads/xj700-bogs-at-high-rpm-under-load.75505/page-2#post-486758
     
    k-moe, Nov 28, 2015
    #2

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