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Firing order

Discussion in 'XJ Technical Chat' started by davy, Mar 20, 2016.

  1. davy

    davy Member

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    Hi guys, Real quick question, What is the firing order of an 81 xj750, I have a Haynes manual and for some reason they think no one wants this information. Thanks.
     
    davy, Mar 20, 2016
    #1
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    firing order of your engine: 1-2-4-3
     
    XJ550H, Mar 20, 2016
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  3. k-moe

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

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    Keep in mind that it's a wasted spark system. 1 and 4 are paired and fire twice every crank revolution, 2 and 3 are also paired and fire twice every crank revolution.
     
    k-moe, Mar 20, 2016
    #3
  4. hogfiddles

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

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    SSSSSHHHHH....... Nobody's supposed to know--_
     
    hogfiddles, Mar 20, 2016
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  5. k-moe

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

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    [​IMG]
     
    k-moe, Mar 20, 2016
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  6. davy

    davy Member

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    Thanks guys, I have two bent valves(3+4) a result of my own stupidity during a rebuild, I will remove all the valves but I am sure it is only 3+4 (already out that are bent).
     
    Last edited: Mar 20, 2016
    davy, Mar 20, 2016
    #6
  7. SQLGuy

    SQLGuy Well-Known Member

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    This actually became relevant for me as I'm in the process of changing the fuel injection to fully-sequential (which involves adding a cam position sensor as well). Google turned up search results that did not agree on firing order, and neither the Haynes or Yamaha manuals actually mentioned it at all. Should have known the correct answer would be here. Also did verify myself, though, by rotating the crank and watching the cams. 1,2,4,3 is correct.

    However, wasted spark systems fire each coil once per crank rotation, not twice. :)
     
    SQLGuy, Dec 19, 2019
    #7

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