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Why wont it idle right?

Discussion in 'XJ Technical Chat' started by newbike91, Aug 20, 2012.

  1. newbike91

    newbike91 Member

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    So I went through the carbs, replaced needles, seats, o-rings, throttle shaft seals, and got nice new pliable airbox to carbon boots. Bench synced and checked float levels, and put them back on the bike. Starts up pretty easily but refuses to idle right. It will stay running but the rpms go up and down all by itself. I tried the mixture screws at 2 1/2, 2 3/4, and 3, and it didn't make much difference. Any ideas? It sounds like someone is reving it up and down without touching the throttle.
     
  2. mwhite74

    mwhite74 Member

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    Sounds like a hunting idle. Are you sure you cleaned the idle passages properly? How are the intake manifolds, any cracks? Even the sync port caps have been known to crack and let air past in some cases.
     
  3. newbike91

    newbike91 Member

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    Sorry a hunting idle? Well there are some small cracks but nothing major I thought. You mean its an air leak?
     
  4. mlew

    mlew Well-Known Member

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    Check for vacuum leaks.
    Do a running sync on the carbs.
    Float levels still might be off, they will cause symptons like you are having.

    Did you check valve clearences?
     
  5. newbike91

    newbike91 Member

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    How do you check for leaks and do a running sync? Haven't done the valve clearances yet its the first day ive had it running since I bought the bike.
     
  6. wizard

    wizard Active Member

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    Check for leaks with an unlit propane torch.
    You need some sort of manometer to carry out a running sync', this could be a home made job or something like a 'carbtune'.
     
  7. Thrasher

    Thrasher Member

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    Adjust valves then sync carbs.
     
  8. newbike91

    newbike91 Member

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    Well I think I solved it. Took the intake rubber boots off to fill some minor cracks with some black silicone gasket maker and discovered they didn't have a gasket between them and the motor. I'm not sure if they are supposed to or not, but I smeared a good layer around the opening and put it back together. Of course its my luck and a float decided to stick and drain gas everywhere but after fixing that and changing the oil it fired right up and idled smoothly. Made me want to jump right on and ride to California. But no, brakes first haha.
     
  9. newbike91

    newbike91 Member

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    Also anyone know how to change the oil without it draining onto the headers? When I take the bolt off it runs right over the exhaust and makes a mess.
     
  10. jeffcoslacker

    jeffcoslacker Member

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    Supposed to be a gasket there. When the silicone fails and starts sucking air, you can cut new gaskets from bulk material ($6/roll) at the parts store...or if you got a patient counterman and don't like to cut gaskets, there are automotive thermostat outlet gaskets that will work, it's trail and error on sizing.

    When I worked at the parts store we had a big Fel-Pro pegboard with all the common t-stat outlet gaskets on it...so it was easy to size them. Now a lotta places don't have that anymore, they sell individually wrapped single gaskets by part number. But ones like NAPA might.

    New gaskets from the bike dealer are like $11/each x 4 for them. No way.

    Have the bike on the centerstand when changing the oil? that should tip it forward enough to keep the oil away from the exhaust...
     
  11. newbike91

    newbike91 Member

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    Oh well that explains it, my bike doesn't have the center stand. Was like that when I got it. And that's what I thought I guess I will make some gaskets.
     

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