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Rubber carb joints (XJ750) - Repair rather than replace?

Discussion in 'XJ Technical Chat' started by tosoutherncars, Apr 10, 2014.

  1. tosoutherncars

    tosoutherncars Member

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    Hey all,

    I've had an XJ for all of three days, so bear with me.

    The bike is an '83 Seca 750. It has been running recently, but is hard to start, and has a bit of a miss at idle. (More than that, I can't tell you.) I am midway through doing the valve adjustment, after which I assume I'll need to do the 'Nine Yards' carb treatment.

    On to my question: I understand that the "carburetor joints" - the rubber pieces between the carbs and the head - are a potential source of intake leaks, which would cause that cylinder to run lean / hot.

    On my bike, a superficial look shows that #1 and #4 are checked / have small cracks; #2 and #3 look pretty good. I'm guessing they're not UV

    Now, as I understand it, there are two part numbers; slightly different shapes? Inner and outer? Are they A / B / B / A, or A / A / B / B or A / B / A / B?

    Anyway... I was a little shocked to find out these things are $80 a piece! Before I drop an extra $320 on the bike... Has anyone tried sealing the carb joints, to prolong their life? I was thinking rubber cement, rubber paint, self-sealing tape?

    Stock pic attached, just so we're all talking about the same thing.
     

    Attached Files:

  2. lacucaracha

    lacucaracha Member

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    The cracks probably don't go all the way through. have you checked? Mine are ugly on the outside, but don't leak one bit. There is a mess of stuff you could try to make it look better, but it won't change much.
     
  3. wizard

    wizard Active Member

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    Bicycle inner tube bedded on clear silicone, makes a neat repair, but if you have the beans buy new.
     
  4. FtUp

    FtUp Well-Known Member

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    have you checked with chacal about the parts? $80 a piece seems awful steep.

    CN
     
  5. tosoutherncars

    tosoutherncars Member

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    Cool, thanks for the replies guys.
     
  6. jablze33

    jablze33 Member

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    Hi temp silicone went on mine an is fine for now til I buy new.
     
  7. jablze33

    jablze33 Member

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    Hi temp silicone went on mine an is fine for now til I buy new.
     
  8. vashtsdaytona

    vashtsdaytona Active Member

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    repair is fine by me, but if your curious the cheapest I have found for genuine Yamaha ones is 45ish partshark.com also I think there is an ebay seller too. plus another 5ish for the gasket to head side.
     
  9. RickCoMatic

    RickCoMatic Well-Known Member

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    Warning:

    Attempting to remove Intake Manifolds from the Cylinder Head has a VERY Serious down-side.

    The Manifolds are fastened to the Head with Non-hardened Steel Cap Screws.
    More often than not, ... they are seized do to Galvanic Corrosion. Sometimes referred to as "Galling".

    They will act like they are being removed.
    But, they twist easily and sheer right off.

    Breaking an Intake Bolt is the beginning of an avalanche of headaches.


    Ask anyone who has broken one off.
     
  10. mtnbikecrazy55

    mtnbikecrazy55 Active Member

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    X2

    But as others have said, the cracks probably do not go all the way through.

    Spray some starting fluid on/around the boots with the bike running, if the rpms change, you have a leak. If not, you're all good for now.
     
  11. BaldWonder

    BaldWonder Innocent Bystander

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    I just talked about this yesterday in my thread:

    I used regular old bicycle inner tube from Walmart. I got the biggest one I could (though diameter of the wheel doesn't seem to change the cross-section diameter of the tube itself). I also bought Silicone caulk/glue/sealant to put in between the tube and the boot, but it's so tight on there that it would have been a sticky mess. Glue would have been everywhere. I opted to leave it at just the tube + boot until it becomes a problem again.

    I would suggest starting with the tube right-side out, and inverting it as you roll it on. The outside is essentially tacky, and the inside is treated with a powder to keep it from sticking to itself. Dragging it on without flipping it inside out is really tough, but inverting it lets you take advantage of the powder.

    Also, you'll have to get clever when it comes to making a hole for the stems. Poking a hole, then stretching, tends to lead to tearing the hole bigger if not clean through. I waited until I had pulled up enough slack that I could poke a hole and place it with the least tugging.

    Oh, and take the caps off the stems as you do this!

    Also,
    It should also be noted that I cut the section long so that I could trim off excess when I was done wrestling with it. Minus the hole-punch part, the end result should look like this.
    [​IMG][/quote]
     
    wgul likes this.
  12. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Mine are all horribly cracked (both 550s) but none of the cracks go all the way through so I packed them with black adhesive RTV and they've been fine for over 4 seasons now.

    On the YICS-motor bikes, the manifolds are oriented / / \ \ (as in the pic above) which is why there are two part numbers.
     
  13. hogfiddles

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

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    inner tube and black rtv is my preferred way. BTW, Baldy....you did a very nice job with yours!

    dave
     
  14. BaldWonder

    BaldWonder Innocent Bystander

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    Muchas gracias, Señor Fiddles.
     
  15. Wirehairs

    Wirehairs Member

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    Doesn't look like anyone posted the original boot repair thread: http://xjbikes.com/Forums/viewtopic/p=3 ... tml#330799

    Somewhat related and looking at baldwonder's picture about: does it matter if you install your carb's vacuum hose on the 2nd or 3rd boot? I thought the 3rd one was correct, as it's a shorter distance to the tank nipple.
     
  16. Maximphilly2texas

    Maximphilly2texas New Member

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    I found new ones on boats.com. $100 for all 4.
     
  17. Andyam6

    Andyam6 Member

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    Mine's always been on #2 (since before I got it anyway), it's fine
     
  18. BaldWonder

    BaldWonder Innocent Bystander

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    Are you sure it was boats.com?
     
  19. Maximphilly2texas

    Maximphilly2texas New Member

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    Very sorry. I found my receipt. It was boats.net and they were $199
     
  20. BaldWonder

    BaldWonder Innocent Bystander

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    Here's the diagram for a 1982 XJ650J.

    I find it interesting that the diagram shows boot #3 as not having a stem cap. I don't doubt that pulling vacuum from any of them is probably fine, but nice to see possible confirmation that it was designed to be #3.
     

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