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Something else to look for when you can't sync / bad idle

Discussion in 'XJ Technical Chat' started by KrS14, May 7, 2013.

  1. KrS14

    KrS14 Active Member

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    I can't believe I haven't noticed this for 2 years lol.

    I took my carbs off on Sunday and spent a good 8 hours going over them piece by piece. Checking:

    ALL jets, emulsion tubes pilot circuits, the "whole 9 yards". Splitting the rack and all that good stuff.

    I first noticed the throttle shafts on #1&2 carbs looks very *scratched* or worn, meaning you could tell there has been quite a bit of friction/rubbing happening on them.

    Upon reassembly I noticed my #1 and #2 carb, throttle shafts (the actual shaft itself) had worn out of spec. Meaning that the diameter of the shaft had been worn down, and it moved the whole butterfly on 1 & 2, when assembled, just by touching the sync assembly.

    It was bad enough that the shaft seals wouldn't make up for the play. The seals themselves are only 2 years old and were in pristine condition.

    This is an issue because when you try to sync these two carbs with eachother, AND with 3-4 any little adjustment will make the butterfly valve move at least a 1/2 mm or so, just in play.

    So if you've done everything you're supposed to do, and get lumpy idle, or impossible sync conditions, check your shafts for play, it will be impossible to get a 100% perfect idle if these shafts have been worn.

    End result is on "ok" idle, but inconsitant, not as good as i'd like, a little 8 stroking every 5 seconds or so. Also when coming off idle, you'll notice 2 cylinders pickup power a little ahead of the other two.

    Just something I noticed, and had never read on the forum here I thought should be brought to attention.
     
  2. hogfiddles

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

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    We talk about throttle shafts a LOT.

    Dave
     
  3. KrS14

    KrS14 Active Member

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    But we don't talk about them being worn to the point of it being a problem, is what I meant hog ;)
     
  4. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    I would think the relatively soft metal of the carb body would wear before the shaft itself.
     
  5. livingdeadlyxj650

    livingdeadlyxj650 Member

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    X2
     
  6. jpacman

    jpacman Member

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    Re: Something else to look for when you can't sync / bad idl

    Can this throttle shaft wear be partly avoided by cleaning and lubricating the shaft pivots? What would you guys use? Recommend?
     
  7. ilyamer

    ilyamer New Member

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    The Carb bodies are made from aluminum, while the throttle shafts are steel... the shafts should not be wearing down before the bodies. If you want to make sure, use a micrometer to test the diameter of the shaft where it is in contact with the Carb and where it isn't, realistically you shouldn't see much fluctuation. I think you're in for some new Carb bodies, unfortunately.
     
  8. hogfiddles

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

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    Oh....ok. Gotcha.

    Now, if the throttle shaft seals are replaced in timely manners, though..... there should be no wear as the seal will hold the shaft at the right position for clearance tolerances while still maintaining the rubber-to-metal seal. As the rubber hardens then the shaft loses the seal support.

    Dave F
     
  9. KrS14

    KrS14 Active Member

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    That does make sense that it would be the bodies that would wear first. It's the body on the inside of the shaft seal that's going, about 1/4 inch or so. That does explain why my #1 and 2 are always so lean. I thought it may be the shafts first cause they look the worst.

    I'll just make due till it dies or I sell it for a new bike. Unless I can find a rack for super cheap on kijiji.
     

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