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carb slide rotating?

Discussion in 'The Garage' started by fullercameron, Aug 31, 2011.

  1. Has anyone ever experienced a carb slide rotating in the carb? I have a set of JBM diaphragms and I pulled the carb off to do some work and the slides seem to have rotated so that the cut-away was facing toward the outside of the bike. The diaphragms are a slip fit w/ no adhesive. Should I use something to stick the diaphragm to the slide so that it can't move independently? If so, what should I use?

  2. cros36

    cros36 thread killer

    im having the same problem. so im watching this for sure.
  3. Im waiting on my shipment from JBM so I too will be watching. Maby ill hit it with some rubber cement right off the bat.
  4. jchrisk1

    jchrisk1 XS650 Junkie

    I am dealing with the same thing. I'm not sure what the problem is. Mine is only turned sideways, and it's only one of them. When I first got the bike it was like that, so I put in new diaphragms and realigned it. Today I took my carbs off and the same side was turned.
    I think I am just going to glue it with some cyanoacrylate glue and see how it does.
    I am curious as to what causes this.
  5. cros36

    cros36 thread killer

    only one of mine is doing it as well, i dont remember which one, as my bike is again in pieces. i tried my hardest to set it completely straight, i think as the air passes under the slide if it is turned a little then its being turned by the airforce? im sure there is a word for it. and its gotta effect airflow and performance.
  6. See below - accidentally posted twice.
    Last edited: Aug 31, 2011
  7. Mine has been having carb issues some to begin with. I had a leaky float valve that was causing my left cylinder to carbon foul plugs like a mother. I got the parts today and realized that this was happening. Since I was running so rich, I couldn't tell if this was causing any real performance problems. I just thought that the slide moving like that would likely block some of the airflow making the bike run richer.

    It seemed like the diaphragms were a tight fit when I put them on, but when I took the carb off today, the bike was pretty warm and it seemed as though the rubber was warm enough to expand to the point that it let the slide turn inside the rubber tire. At first I thought that it was twisted because it didn't have the keyed section like the stock unit did, but I had marked the fronts of the diaphragm and slides with a bit of white paint marker and I could see that the diaphragm had not twisted - the slide definitely moved inside the diaphragm.

    They were both this way. I was just trying to figure out what type of adhesive would be flexible enough and able to deal with the conditions found inside a carburetor. I thought that cyanoacrylate glue like super glue would be too brittle and might fail. I was thinking more along the lines of a tiny dot of rtv or silicone or something?

    Ha anyone noticed any performance loss that has seen this happen?
  8. Just checked the website for JBM. Says in the installation instructions that super glue will work but that they don't think it is necessary.

    I might stick a little on there tonight or tomorrow and see if this fixes the problem.
  9. cros36

    cros36 thread killer

    maybe someone should email him and let him know what going on. i dont want to bombard him with shitty emails cause he is a great and helpful dude to talk to. and his shit is good, his manifolds hold my carbs unsupported and his diaphrams seems good besides this little problem. what do you guys think?
  10. I agree the diaphragms are great and a really good price. Saved me a bunch not having to buy completely new slides.

    I thought I might give him a call, but I agree he probably doesn't need ten calls.

    If someone is psyched to make the call and feels like they have the technical know how to explain this really well, let me know, otherwise I might just give him a shout tomorrow.
    Last edited: Aug 31, 2011
  11. cros36

    cros36 thread killer

    hey fullercameron, just reread your last post about the brittle superglue. if some breaks off it could bounce around on the diaphragm causing some other problems with wear if it get caught between a fold in the diaphragm.
  12. cros36

    cros36 thread killer

    you call and let us know whats up.(if you want) its great this came up, i kinda forgot about it.
  13. Guy seemed really nice and helpful when I first spoke to him. When I called a couple days later asking for a tracking number he wasnt very helpful. Maby he was stressed, I dunno. Im gonna go with some super glue when they finally show up. been a week now.
  14. jchrisk1

    jchrisk1 XS650 Junkie

    I don't think it would be a problem. I've used super glue, in a pinch during live shows, to fix speakers that were taking way more abuse than these diaphragms could ever see.
    I think if you sand the lip at the top of the slide, push the diaphragm up to it and run a bead around it, it will be fine.
  15. cros36

    cros36 thread killer

    my old guitarist got drunk one night before a show and cut the shit out of his finger, he used superglue to fix it up. good story right?
  16. Went ahead and put a drop of glue on the crack between the slide and diaphragm from the top side and turned the diaphragm back and forth a time or two to get it to wick into the crack. Let it sit for ten minutes and then put it back together. Seems to have stuck well. I just wiped the down before adhering everything.

    I'll let you know if the glue seems to hold or not.

    In the meantime, I'll try to give him a shout tomorrow when I have some time and let him know that a number of people have seen this happening and see what he says.

    Report back soon.
  17. jchrisk1

    jchrisk1 XS650 Junkie

    We always used super glue to glue fingernails back to fingers from bending strings. Sometimes it's the only way to keep playing. But if I had a guitar player that got drunk before shows, he would not be in the band very long. Guitar players are a dime a dozen. Easily replaceable.

    Do you know how many guitar players it takes to change a light bulb?

    Ten. One to actually change the bulb, and nine to stand around talking about how they could have done it better.

    What's the difference between a guitar player and a terrorist?

    You can negotiate with a terrorist.
  18. I've encountered BS 38's with slide's that have rotated a number of times and found this problem not to be caused by or associated with the diaphragm...Whether the OEM type swaged in between the two nylon rings or the JBM DIY one piece molded in snap fit integral rubber washer design.

    Rather, I've found that the rotation of the slide seems to be occurring when the slide surface comes in contact with some desposit, debris or damage on one side or the bore other as it travels up and down. This gunk deposit can be quite hard and stuck to the slide surface itself or more likely....the inner surface of the slide cylinder bore in which the slide travels up and down. Usually it's intake air carried deposits on the aluminum cylinder wall near the top. I suspect this gunk to most likely be from crankcase gas vented through the breather tubes to the air boxes and thence into the top oblong air intake port in the carb throat bell and then to the CV diaphragm chamber, slide and bore.


    Locate and remove the interference (that is causing the slide to rotate) by gentle cleaning preferentially to trying rotation restriction by gluing the diaphragm to the slide

    Usually fairly easy to detect and correct by careful removal cleaning and deposit elimination.....

    1. Remove the 4 screws of the cylinder top cap and remove cap & slide spring

    2. Carefully loosen the diaphragm from it's perimeter groove in the slide cylinder body and remove it together with the slide assembly. Examine the slide surface for dirt, deposits or damage. Clean with a soft clean cloth (tee shirt, cheese cloth etc.) and WD 40.

    3. Carefully examine the now exposed entire polished aluminum surface of the cylinder bore by both sight and feel. I've usually detected a ridge like bonded piece of glue-like varnish near the top edge which can usually be softened and wiped out with a soft cloth and WD40. I've also used a small dab of chrome polish like Simichrome to clean off the deposit spots and also to carefully & gently re-polish the smooth surface of the bore aflter cleaning. No abrasives or metal removal! Sometimes feel detects the crud or deposit spots for cleaning better than sight.

    Gently clean and re-assemble, test for smoothness of slide operation. The "rotating slide problem" is usually solved. A very slight amount of cyano acrylate (super-glue) can be applied between the rubber tire of the diaphragm slide metal groove to help prevent rotation if you wish but; don't get any on either the slide surface or cylinder bore!

    Sorry No Pictures! Hope I've made it clear ask away if not. I happened to be doing some carb sets now and fixed two such gunk spot infected bores with rotated slides today. Of the 10 or so used BS 38 carb sets I've purchased and tried to set right, I guess I've encountered 6 or 7 individual carbs with the problem. So far, all have been corrected by the process described. Moreover, I prefer not to bond the diaphragm to the slide.

    BTW....You can probably guess how I feel about the venting of dirty oil laden crankcase breather tube gases into the air filter boxes and therefore into the carbs and CV chambers but; that's an EPA emissions matter as you might guess...ahem. Blue
    Last edited: Sep 3, 2011
    gggGary likes this.
  19. jchrisk1

    jchrisk1 XS650 Junkie

    Thanks for chiming in blue. You have explained it perfectly clear. I will check that out tomorrow and see what I find.
  20. Removing the cause of slide rotation continued....
    Ran across some additional pics that may be of use in locating the spots that most frequently get fouled with deposits and interfere with CV slide movement and cause rotation. Perhaps they'll help?

    The portion of the CV slide bore that seems to get most of the gunk deposits is the bottom right quadrant of the cylinder between the oblong air intake slot and the round outlet hole say 6 to 3 o'clock. Down over the top edge into the slide bore 1/4 to 1/2 inch.

    You'll probably feel the hardened gunk spots easier than seeing them....Blue

    Attached Files:

    Last edited: Sep 9, 2011
    gggGary likes this.

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