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Misfire and no idle

Discussion in 'XJ Technical Chat' started by Scorpion1016, Jul 11, 2017.

  1. Scorpion1016

    Scorpion1016 Member

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    Hey everyone my 81 seca 750 misfires or backfires on all cylinders. I have checked the plugs coils wires tci box and everything with the ignition system. They all seem good. I tore the carbs apart to see if their were any issues i took off the top hat air jets fuel jets slide and the emulsion tube. i am unsure of where i am going wrong. When i try to tune it with the gunson color tune it runs blue then flashes bright white then right back to blue for all cylinders. Any help would be greatly appreciated. I've been stumped for about a month now.
     
  2. fiveofakind

    fiveofakind Well-Known Member

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    1. Get Your valves in spec.
    2. Full teardown of carbs,
    3. Bench Sync
    4. Vacuum Sync
    5. Colortune plugs....
     
  3. Chitwood

    Chitwood Well-Known Member

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    ^^^that. Also, did you break out a meter to check over the ignition system or simply do a visual check? A multimeter will tell you a lot
     
  4. Scorpion1016

    Scorpion1016 Member

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    I have done the valves the carbs were taken apart except the choke circuit every thing else taken apart and cleaned. The carbs are bench synced all have the same butterfly clearance. And every thing is within ohm spec coils are new along with wires caps
     
  5. tabaka45

    tabaka45 Well-Known Member

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    Get the white out. You may be a little too lean.
     
  6. kerriskandiesinc

    kerriskandiesinc Active Member

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    Valves in spec??
     
  7. Chitwood

    Chitwood Well-Known Member

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    The way you describe the colortune being nice and blue then flashing to white sounds like a fuel delivery issue. Have you checked for vacuum leaks? Replaced throttle shaft seals when carbs were apart? This requires "breaking the rack". If you have not done so I highly recommend taking the carbs to church. I'm sure someone with the proper know how will come along and provide a link for you
     
  8. fiveofakind

    fiveofakind Well-Known Member

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  9. XJ550H

    XJ550H Well-Known Member Premium Member

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    set your petcock to prime and see if it still has the issue that will/should give you a steady fuel flow.
    have you wet set or checked the fuel level in the carbs?

    Setting the fuel levels

    airbox or pods?

    next time you have the carbs off clean the enrichment circuits.
    try giving it a little choke and see what happens.
     
    Last edited: Jul 11, 2017
  10. Scorpion1016

    Scorpion1016 Member

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    Choke makes the bike run but rev to the moon and I have the air box can't even imagine tuning pods the fuel levels are good in the carbs right now I have a test tank on it with the vacuum line plugged off their are no vacuum leaks as far as I can tell I have repaired the rubber boots
     
  11. tabaka45

    tabaka45 Well-Known Member

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    Sounds like you are running a little lean--especially since choke helps. Therefor, open the pilot screws about the width of a dime and see what happens. Do this several times if necessary. What do your plugs look like? If this doesn't help, then it's time to pull the carbs and pay special attention to the pilot/enrichment circuit.
     
  12. Scorpion1016

    Scorpion1016 Member

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    I'm not totally sure what the enrichment circuit is. Is that the tube that follows the pilot jets
     
  13. fiveofakind

    fiveofakind Well-Known Member

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    Part of the Enrichment ( Choke ) circuit is in the float bowl ( the well ) .......Chacal sells a drill bit for cleaning this well.......highly suggested to buy it.....sure makes cleaning it a lot easier.....

    Do you see that passageway at the bottom.....it goes down & angles at a 45 degree angle......you need to get this passageway cleaned out for proper cold starting in the mornings....

    http://www.xjbikes.com/forums/threads/how-to-clean-the-enrichment-circuit-well.8918/

    [​IMG]

    Do you see that brass tube ...that goes down into the passageway in the float bowl.....that needs to open also...use the drill bit to open if clogged...
    [​IMG]
     
    Last edited: Jul 12, 2017
  14. Scorpion1016

    Scorpion1016 Member

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    Thanks for the help everyone never had a bike with carbs this complex
     
  15. fiveofakind

    fiveofakind Well-Known Member

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    that what inline 4's are all about.....4 carb's ........ouch....

    Also not a bad idea to disassemble the choke hardware up top.....& clean up your choke plunger & springs and that passageway.....easy stuff here......

    We will get you thru this......no worries...be riding......
     
  16. tabaka45

    tabaka45 Well-Known Member

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    be darn careful when sticking anything in the carb passages. If you can ultrasonic clean them I would try that first. Mess up a passage and you're in deep dodo.
     
  17. fiveofakind

    fiveofakind Well-Known Member

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    I never had a problem sticking drill bits in the passageways to clean them out......especially the enrichment choke well.......

    Never needed to ultrasonic clean or chemical dip them.......
     
  18. Polock

    Polock Well-Known Member

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    i use a .013 steel guitar string to clean those out, and a lot of patience. use the little red tube on a can of brake cleaner to test if it's clear
     
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  19. XJ550H

    XJ550H Well-Known Member Premium Member

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  20. k-moe

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

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    Throttle

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