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carb problem

Discussion in 'XJ Technical Chat' started by Steve Noltensmeyer, Jun 30, 2025 at 4:25 PM.

  1. Steve Noltensmeyer

    Steve Noltensmeyer New Member

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    I need suggestions where to go from here

    81 Yamaha XJ650 Maxim
    I just completed rebuilding my carbs.
    I tore them down completely
    broke the carbs apart into individual carbs
    removed everything jets etc...
    used carb cleaner, wire tool, and air to clean all passages
    ultra sound cleaned carbs
    soda blasted carbs
    cleaned all with carb cleaner
    reassembled

    The bike started up within a second or two on prime / switched to on
    i set the idle / idles at 700 well
    revs and snaps back

    I start on a test ride and it bogs when accelerating hard

    I got brand new gas
    I changed the oil
    I changed the spark plugs
    I put seafoam in gas
    I tried turning fuel mixture screw in 1/2 turn all 4 carbs
    I tried turning fuel mixture screw out 1/2 turn all 4 carbs
    I tried running in prime petcock
    I tried running in reserve petcock

    It seems better after spark plugs were changed / but still not strong acceleration / some popping not much
    It sounds good revving in neutral

    I need suggestions where to go from here

    the bike was running good before I started / but leaking gas
    I replaced the needle and seat
    I replaced the O-rings in the gas pipes between the carbs / this was the problem I think / no gas leaking now

    Thank you in advance for any advice you have for me.

    I have rebuilt / clean carbs on this bike several times and on my 81 Honda CB750K many more times than I like to admit.

    Stevenolts
     
  2. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Did you bench sync the carbs on assembly and then do a running sync with gauges?
     
  3. hogfiddles

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

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    I don’t see anything about syncing, or float height, or colortuning…….
     
    Rooster53 likes this.
  4. Steve Noltensmeyer

    Steve Noltensmeyer New Member

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    what is color tuning?
    I will sync the carbs / that was next on my list / I have sync tool /
    If I need to take the carbs back off I will check the float height

    Thank you!!!

    This carb ran great on the bike when I took it off
    it was cleaned about a year ago
    it was leaking so I figured if I was taking it off to replace the O rings in the carb connection pipes I would clean extra good this time
     
  5. cds1984

    cds1984 Well-Known Member

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  6. Rooster53

    Rooster53 Well-Known Member Premium Member

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    hogfiddles likes this.
  7. Minimutly

    Minimutly Well-Known Member

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    If you log on and click the xjforever icon top right, you can access a mine of information, including carb setting and cleaning. As well as searchings on carbs issues. You will quickly gather that 90% of issues with these old bikes is carb related, sometimes because they are old, dirty, or issues caused by owners. They are all vacuum operated devices, and little understood. Even when you do understand them, they can take a while to sort.
     
  8. Steve Noltensmeyer

    Steve Noltensmeyer New Member

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    Thank you for your advice
    I am off tomorrow
    I will take another look

    Thank you,
    Stevenolts
     
  9. Timbox

    Timbox Well-Known Member

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    Did you do an air pressure check to make sure the diaphragms were seated? That too would cause bog issue.
     

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