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Bench synching a 550

Discussion in 'XJ Technical Chat' started by DarthBob, Apr 1, 2007.

  1. DarthBob

    DarthBob Member

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    The carbs are off the bike, and when held up to the light, there's a noticeable difference in the sizes of the smiles that the butterflies make.

    I have my manometer ready to synch but I'd like to bench synch before I put them on. Previous posts indicate that you open the manual idle screw until you can fit a spray tube from a can of WD-40 under the #3 butterfly, but on the Mikuni's, I can turn the idle adjustment rod all the way open and its still too small to fit a tube.

    Anyone have any idea what else I can use to bench synch? feeler guage, nail, drill bit? A hair, of the short and curly variety?
     
  2. gremlin484

    gremlin484 Member

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    If you have your manometer, it shouldn't be too hard to sync them once you get them on the bike... As long as you get them close.

    I bench synched mine visually... Just making sure they all looked about the same. After putting them back on the bike, and hooking up the manometer, ( which I made from 4 long tubes, all connected at the end, with transmission fluid as a guage ) and started the engine, one of the cylinders (either 2 or 3) started sucking the fluid up right away. A quick kill, a turn of the adjusting screw later, and a restart, and they were all ready for precision syncing.

    Really, being precise when bench syncing is important if you do not have a manometer. If you got one, just fudge it and sync with the gauge.
     
  3. DarthBob

    DarthBob Member

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    The synch is way off, I'd like to bench synch it so it will start, run, and idle easier for the more precise synching with the manometer. Previously it was surging all over the place when trying to idle, which was due partly to the holy boots I just replaced, but I'm guessing it was also partly due them being out of synch.
     
  4. BlueMaxim

    BlueMaxim Active Member

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    You just need something that will fit. I would try a solid copper wire or a small nail.
     
  5. DarthBob

    DarthBob Member

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    So it doesn't matter how much they're open as long as they're all open the same. I can't believe I had to ask about this :oops:
     
  6. Captainkirk

    Captainkirk Member

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    They really don't have to be open much. If you can't adjust them to a WD-40 nozzle then don't worry about it; adjust them so they're equal and go from there. If you have the manometer, that's the important part.
     
  7. DarthBob

    DarthBob Member

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    I did a search and the WD-40 tube was one of the first methods I found, had I kept going, I would have seen the ones suggesting twist ties, wires, drill bits etc. And to top it off, while looking for something small guage to use, I found my feeler gauges!
     
  8. RickCoMatic

    RickCoMatic Well-Known Member

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    Well ... if you really need a small diameter ... you can always run-out and get a strip of PlastiGauge.

    Pop rivit, finishing nail, 100 Pound Test Mono-filament, the Ground wire stripped out of some Romex, Bic Pen innards ... round and small!
     
  9. carsonschaos

    carsonschaos Member

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    Good timing on the thread. Just came in from the garage.
    I bench synched my carbs by looking at the small fuel holes.
    After putting them on the bike and using the tube methed.
    The carbs were really not that close according to the tubes.
    By not close, I mean the tranny fluid inched up the tube about an inch or so in 5 or 10 seconds.
    Maybe a half to a turn to correct.
    I assume that it's not unnormal for the bench synch to be off a turn.
    I'm letting it cool alittle and will test again.
     
  10. wingnut325

    wingnut325 Member

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    Take the wire out of the little twist tyes for the loaf of bread or garbage bages. Use it like a feeler gage. Adjust them down until you feel the same amout of drag from each carb. Don't be suprised if the idel is real high after you get them on. Just adjust it with the regular adjustment.
     
  11. Hired_Goon

    Hired_Goon Member

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    No, that's pretty normal and pretty good for a bench sync to have it that close.

    Letting it cool for a while is good if it's been running for a while, but remember it should be synced at operating temp.
     
  12. aj173pa

    aj173pa Member

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    When your using the manometer is it nessecary to use the YCIS tool at the same time?

    81 XJ550
     
  13. BlueMaxim

    BlueMaxim Active Member

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    Yes. You can sync without it but best results are with it in.
     

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