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  1. #1
    steve45's Avatar
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    O-Rings For CV Carbs

    In another thread, I mentioned that I'm going through the carbs on my STXs, also on my Ultra 150. There are 16 O-rings on the fuel rails, and it turns out that the O-rings on the needle valve seat are also the same, total of 19 O-rings all together.

    I ordered the required 57 O-rings from Kawasaki at an astounding cost of about $115. What a rip-off! Anyway, I got thinking that there has to be a better material for these things that will hold up with ethanol. I searched various suppliers and manufacturers. Of course, the O-rings are NOT a standard SAE or metric size... I also looked through tables of chemical compatibility and found that EPDM is probably the best material to use. I contacted one manufacturer about getting a run of custom O-rings made. For some reason, they did NOT recommend the EPDM material, but rather Viton. I'm having an email discussion with them now, as their own chart shows that Viton does not play well with ethanol.

    Anyway, they are talking of approximately $500 for a production run of 5000 O-rings. I'm trying to judge if it's worth pursuing, assuming we can get a material that WILL be compatible. If I sold them at $1 apiece (HALF of Kawasaki's price), I'd break even after selling 26 sets.

    So, is anybody interested?


  2. #2
    Click avatar for tech links/info K447's Avatar
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    How did you determine the exact size needed for new non-OEM o-rings?

  3. #3
    steve45's Avatar
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    Quote Originally Posted by K447 View Post
    How did you determine the exact size needed for new non-OEM o-rings?


    I measured them as accurately as I could with a micrometer. Prior to actually having some manufactured, I would send them a new one as a sample.

    The dimensions I came up with were 0.050" thickness x 0.270" ID.

  4. #4
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by steve45 View Post
    I measured them as accurately as I could with a micrometer. Prior to actually having some manufactured, I would send them a new one as a sample.

    The dimensions I came up with were 0.050" thickness x 0.270" ID.
    Can you also measure the ID and OD of the ring grooves where they fit into?

    Regarding new sending o-ring samples for sizing,I would suggest sending several, not just one. Variances in ring sample size might be useful to know.

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  6. #5
    steve45's Avatar
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    I can measure the grooves, but all the O-ring specs I've seen give actual O-ring dimensions, not groove size. I'm guessing a durometer rating of about 70-75.

    Yes, I would actually send a couple of samples.

    When I compared the needle valve seat to the fuel rail, I measured the grooves. They were within about .001"-.002", which is smaller than the tolerance on most O-rings.

  7. #6
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by steve45 View Post
    I can measure the grooves, but all the O-ring specs I've seen give actual O-ring dimensions, not groove size. I'm guessing a durometer rating of about 70-75.

    Yes, I would actually send a couple of samples.

    When I compared the needle valve seat to the fuel rail, I measured the grooves. They were within about .001"-.002", which is smaller than the tolerance on most O-rings.
    I expect the manufacturer would find the groove info useful, even if just to confirm the target dimensions from measuring the OEM samples.

  8. #7

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    I'd buy a set.

  9. #8
    I would also

  10. #9
    steve45's Avatar
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    I heard back from the manufacturer. He said that, indeed, Viton is the best choice for gasohol. He said that the other additives in gasoline tear up the EPDM. It does seem to me that the Viton tips on the needle valves hold up a lot better than the O-rings.

    He also said that we could get them in brown, to differentiate them from the standard O-rings. He again said that the cost would be about $500-600 for 'a few thousand'. He didn't give me a specific price yet.

    I asked if there was a way to test the OEM O-rings to see what material they were actually made of and he said that the cost would be astronomical. He said most of the old fuel system O-rings were made of Buna N.

  11. #10

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    Why not just buy them from McMaster Carr? Are they a size that they don't have?

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