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Carb trouble again.

Discussion in 'XJ Technical Chat' started by Jake750, Jun 30, 2022.

  1. Jake750

    Jake750 Member

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    Hey guys. So my radian 600 was running like crap. If the bike was in neutral it would rev normally but any load on it what so ever and it could barely get the rpm’s past 5-6k with absolutely no torque.

    figured something was up with the carbs. Resynced them but the problem persisted. Removed them and opened them up, turns out the PO used aftermarket needles and had the needle clip setting not where it was supposed to be. I managed to track down a set of oem needles.

    finally got them put back together. One thing I noticed is that on 3 of the carbs, when I lift the carb cylinder up with a finger, they come down quick with a satisfying “clunk.” On one of them, however, the carb slide and needle takes significantly longer to come back down and dosnt clunk like the other ones.

    is it a problem that one of my carb slides is doing this?

    thanks in advance.
     
  2. k-moe

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

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    Were you lifting them with the carb hats on, or off?
    They should all drop at the same rate with the diaphrams in place and the carb hats on, and should not clunk.
    The clunk test is done with the carb hats off, and the slides should fall quickly.
    If you have a slow slide with the carb hats off, then the bore for that slide needs to be cleaned and lightly polished. DO NOT polish the slide itself, as that will remove the plating from it, leading to even more trouble.
     
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  3. Jake750

    Jake750 Member

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    Carb hats on. So that means that only one is working properly? What is the remedy for clunking carb slides with hats on??
     
  4. Rooster53

    Rooster53 Well-Known Member Premium Member

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    So there is normally no clunk with the carb hat on because the diaphragm is working.

    It may be you only have one carb that is actually functioning and lifting the slide effectively running the bike on one cylinder with a huge reduction in power.

    Check that the rubber diaphragms are installed correctly in their grooves, if so look for tears or pin holes in the diaphragms

    I think you can test them with a shop vac by pulling air through the venturi with the throttle plate open
     
    Last edited: Jul 1, 2022
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  5. Timbox

    Timbox Well-Known Member

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    Jake,
    Sounds like you will be taking the carbs off again. When you test them this time I would do a diaphragm check with some compress air. If you have that at hand, you can push compressed air into the carbs from air box side. If the slides are working right, you will see them rise and fall with the air pressure.

    Start slow with the air pressure and work your way up to what is needed to make them rise and fall. Just one against the other and make sure they are all working right. Some times when putting the hats on I have missed making a good seal with the diaphragm on the top of the carb.
     
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  6. k-moe

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

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    If you don’t have an air compressor you can use a vacuum cleaner on the engine side of the carbs. It doesn’t have to be a shop vac.
     
  7. Jake750

    Jake750 Member

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    I am going to try the air compressor or vacuum test when I get home. It seems that the carb diaphragm rubber on the 3 carbs that dont want to seal is noticeably less elastic. It feels less stretchy and dried out or kinda brittle. No pin holes or tears that I can see. But they are "Crinkled". Like paper that has been crumbled up. There are creases in them. Is this common with old carb diaphragms? Assuming that is the problem, anyone have any recommendations for rejuvenating the rubber. After a quick google, i found that people recommend soaking the rubbing in glycerin. Any thoughts?
     
  8. Timbox

    Timbox Well-Known Member

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    Well yes and not. It is hit of miss if you can bring them back to life. I have used both of these methods to try to bring some life back:

    1. Is just coating the rubber with some mystery oil, the stuff in the red container.

    2. Here is a link from another forum on how to bring rubber boots back to life, it could work too. https://v4musclebike.com/forums/showthread.php?t=13477

    If you have to, you can always buy new diaphragms and replace them. Have done that a time or two.
     
  9. Jake750

    Jake750 Member

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    I'm going to bite the bullet and try to just replace them instead of taking my chances with trying to "rejuvenate" the rubber.
     

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