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“Droopy” float needle pin

Discussion in 'XJ Technical Chat' started by Cattleman XJ, Apr 24, 2019.

  1. Cattleman XJ

    Cattleman XJ Member

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    So, getting my carbs back together (what a ride this has been) and upon reassemble of the floats/float needles, I’ve got 2 needles in which the little plunger pin that the float frame rests upon is super springy and holds the float assembly up. The other 2 are pretty wimpy. They’ve got some spring to them, but it seems like the spring inside isn’t fully extending and there is a fair amount of free play when I pull the pin all the way up- say, 1-2mm.

    So while I’m sure the answer is “just replace the bad ones while you’re in there, dummy!”, what do these plungers/pins actually do?

    Thanks

    85 XJ700N
     
  2. k-moe

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

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    My understanding is that they are meant to help dampen vibration in order to keep the floats from bouncing around too much. Inpractice that isn't as much of an issue on an inline 4 as it is on a twin.
     
  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    spring keeps pressure on the hole that fuel flows through to fill bowls.
     
  4. Cattleman XJ

    Cattleman XJ Member

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    That would make sense as the needle valve already moves up to make the seal
     
  5. Polock

    Polock Well-Known Member

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    this is a good thing
    this is a bad thing, when the carbs are upside down the full weight of the float should compress them.
    set the stuck ones in a dish of gas over night then hold them under the gas and push the little rod about a million times, it should loosen up.
    you might have to pull the rod out with needle nose to get it started
    don't lose the rubber tip, rubbing compound and a q-tip in the seat till it shines
     
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  6. Cattleman XJ

    Cattleman XJ Member

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    Oh really?

    See, I have been testing them while the rack was upside down. The needles are seated, but the rod holds the float frame up a bit higher on the springy set. To the point where I can push down on the floats and they’ll pop back up to a more midline position. The wimpy ones allow the floats to hang at a lower angle. There is some spring to them, but not nearly the snap or height. So this sounds like they might actually be the ones that function correctly and the others I assumed were good are actually the bad set?

    I’ll post some pictures in a bit
     
  7. Polock

    Polock Well-Known Member

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    the rods should snap right up, working them submerged pumps the goo out. they should all be the same length, out and in.
    when you set the floats dry, tilt the carbs so the float tang just touches the little rod but doesn't push it in. that is where it needs to be when you measure.
    when the full weight of the float is on the pin, the seam on the floats is really close to parallel with the edge of the carb (you'll see what i mean)
     
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  8. Cattleman XJ

    Cattleman XJ Member

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    First pic #4, #3.
    4 has one of the stronger springs and 3 weaker.

    Second pic #2, #1.
    2 stronger, 1 weaker

    Third pic. Closeup of 4 showing it pretty level resting on the pin/plunger/rod.

    Fourth pic, closeup of 3 showing a nose down

    Fifth pic, side by side of needle from 4 next to 3 showing difference in height with 3 resting on the internal spring. I can pull the rod on 3 up easily where it matches 4, but it won’t stay. It’s just dead air between the spring and the seat of the rod where it makes contact.

    So yeah, the stronger needles are holding the floats parallel with the seam. The wimpy ones don’t
     

    Attached Files:

  9. k-moe

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

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    New float needles aren't expensive. @chacal even has some nice all-brass needles.
     
  10. Cattleman XJ

    Cattleman XJ Member

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    @chacal is gonna send me to the poor house :-o
     
  11. k-moe

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

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    No, buying a new Yamaha will do that.
    Frugal does not mean cheap.
     
  12. MattiThundrrr

    MattiThundrrr Not a guru

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    Those Scramblers they haven't been able to sell are getting cheaper and cheaper...
     
  13. k-moe

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

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    Ya. You can only buy 8 running XJ's instead of 9.
     
  14. Ryengoth

    Ryengoth Active Member

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    I have been using www.cmsnl.com to look up the original PN and if there was a succeeded # to it. More often than not there's an aftermarket cross-reference for succeeded numbers that aren't on US dealer sites. I've found a lot of missing part numbers on partzilla and bikebandit but these guys usually have the full OEM list you can use for cross-referencing to make sure you get the right part.
     
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  15. k-moe

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

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    Interesting that they use a picture of a 650 Turbo to represent an XJ750.
    The parts list is good though. The same one that all dealers can give customers access to if they want.
    If you want to see U.S. prices yamahapartshouse.com
    The cross-refrence is not as handy to use though since they don't put that information on the same page as the part.
     
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  16. Cattleman XJ

    Cattleman XJ Member

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    I’m thinking that 2 of them are aftermarket and 2 are original.

    I got all excited when the owner handed me 4-5 boxes of floats only discover that they were for a mikuni carb and not a hitachi.

    Lord knows what needle valves he put in them. All 4 seats are aftermarket for sure
     
  17. Tim O

    Tim O Active Member

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    After trying to set my floats over and over (and over) again...
    Best thing I ever did was let Dave replace the needles and seats with the all metal variety.

    Wet setting was easy when I got them back and in subsequent "touch up" cleanings i think I've only had to readjust one float a very small amount.

    That taught me that the seats and needles are made as a matched set. If you leave them as mix and match I think you'll be chasing your tail for a long time.

    One will get stuck while another floods, etc. Even if they are set correctly...
     
  18. k-moe

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

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    In the case of viton-tipped needles that isn't accurate (and I doubt it's the case for the all-brass needles as well, or they would be match-numbered).
    What can be an issue is if needles or seats of different types (particularly if the manufacturer is not making them to the corect tolerances) are mixed, in which case you will run into trouble. That can also be a problem if the sprung-type have sticky or weak springs in them.
    What can happen is that the needles and seats wear on each other, and can end up not sealing well if they get swapped around, but they tend to need replacement by then anyway.
     
  19. Tim O

    Tim O Active Member

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    :rolleyes: ummmm.... yeah, same end result.

    Change them all to new same manufacturer... or dont... maybe someone enjoys pulling their carbs every two weeks.
     
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  20. Cattleman XJ

    Cattleman XJ Member

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    Alright well I’ll have a set of solid metal needles headed this way by Monday hopefully-plus more goodies.

    This whole process has just reaffirmed my distrust when someone says “yeah, I had a guy I know go through everything”. I’d have been better off had numb-nuts just kept his hands to himself.

    I’m eternally thankful that the guy only touched the carbs and never had possession of the entire bike.
     
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