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  1. #1
    steve45's Avatar
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    Been Doing Some Work On CV Carbs

    I've got an 1100 STX that has burned the front piston twice. I bought it used and was told by the previous owner that the oil line fell off and it was running fine at the time. I was leaving on vacation the day after I got the engine in and I didn't have time to go through the carbs (and didn't see the need). Burned up the piston.

    I opened up the carbs and found trash in them, which I figured was probably responsible for the failure. I cleaned the carbs and the the fuel rails and put it back together. After about 5 hours of break-in, I started to run it hard. It did OK for a while, then seized the front piston again.

    Time to do it right and check pop-off pressures, etc. Tonight I finally had time to work on it again. The pop-off pressure really wasn't well defined, as the O-ring on the needle valve seat leaked badly. It finally popped at about 30 PSI, spec is 15.6 PSI.

    Kawasaki doesn't list the O-ring for the needle valve seat separately, they want to sell you the entire assembly. I got out the micrometer and measured the grooves in the needle seat and the fuel rail tubes and they were virtually the same. This means that you can use the fuel rail O-rings for the needle seat.

    I just wanted to pass this along in case somebody else had the same problem.


  2. #2
    swlamarshrunner's Avatar
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    Good info to know. If anyone comes across this and needs some CV carbs, I have a good set I would sell very cheap.

  3. #3
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by steve45 View Post
    ...

    Kawasaki doesn't list the O-ring for the needle valve seat separately, they want to sell you the entire assembly. I got out the micrometer and measured the grooves in the needle seat and the fuel rail tubes and they were virtually the same. This means that you can use the fuel rail O-rings for the needle seat.

    ...
    What would be the part number for the fuel rail o-ring that also fits the carb needle seat?

  4. #4
    steve45's Avatar
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    O-ring part number is 92055-1246.

    I'm thinking about trying to find an O-ring of the same size that may be more resistant to ethanol.

  5. #5
    Myself's Avatar
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    Steve45, make sure you check out the fuel pump. Worn out/deformed diaphragms will cause that.

  6. #6
    steve45's Avatar
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    Quote Originally Posted by Myself View Post
    Steve45, make sure you check out the fuel pump. Worn out/deformed diaphragms will cause that.
    It's consistently the front cylinder. I was thinking it might also be a leaking seal or gasket. I'll be sure to pressure test the case when I put it back together.

    Have you seen a fuel pump cause a problem on only one cylinder?

  7. #7
    Myself's Avatar
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    Yes, If there is a diaphragm problem everything normally is fine until the higher RPM's. That's when it can't quite pump enough fuel to keep up with demand. It will run lean on front or rear always, never the center. Seen it on Polaris 650/750,Kawi 1100/900, and yamaha 1100.

  8. #8
    steve45's Avatar
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    As old as they are, I might as well replace the diaphragms. Wish you could get parts for the Ultra 150 fuel pumps...

    I've often wondered if you could replace the Ultra 150 fuel pump with an 1100 fuel pump. The fuel consumption isn't that much different, and the pumps are designed to deliver more fuel than the engine requires. Just wondering...

  9. #9
    Myself's Avatar
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    I'm sure Mikuni makes a pump that would keep up with demand.

  10. #10
    steve45's Avatar
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    Update on this particular engine: I had sent the cylinders off to have them cleaned up. The shop called and said that they found a crack in the problem cylinder. They thought it might have been from the previous time it failed, but not sure. I wonder if there was a problem with it for some time and the crack would open up when it got warm. I didn't see the crack before I shipped it off.

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