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  1. #1

    Seadoo Compression Issues

    I have a 1995 Seadoo XP 720 that im having some issues with. I original bought the ski and it ran lean and lost compression in both cylinders. I replaced the following after that happened.

    Replaced all fuel lines
    Replaced Fuel Selector Valve
    Rebuilt Carbs with Mikuni Rebuild kit
    All new top end gaskets
    New bored .5 over cylinders with brand new .5 over pistons and rings

    After all this was completed, I tested compression before I test rode it. It read 130 PSI in both cylinders with a harbor freight tester. The compression tester seems to be good because I used it to test my Polaris and it reads fine. After that I took the ski to the water for a test. I took it easy on it and did plug chops to assure it wasn't running lean and tuned it where it was running great but was really hard to start after it was shut off. I rode it for about a half hour. Once I got back home, I tested the compression again and it dropped to 90 PSI in both cylinders and is still hard to start.

    The ski ran great and hard in the water so im a little confused on what to do next.

    Can anyone help me on what to do next or what might fix it?

  2. #2
    UPDATE! After I tested compression after the lake test the seadoo sat over night and I retested it tonight and compression is back to 120-130 psi which is good for me with the cheap gauge im using. I'm a little confused on why it tested low right after the test ride and tested fine after it say for a day. Any help!?!?

  3. #3
    Hot compression is always lower than cold due to oil viscosity. I've never seen it drop that much between hot and cold though.

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  5. #4
    Mpeavler's Avatar
    Join Date
    Dec 2005
    Anderson, Indiana
    Did you break in the new pistons and rings ? What was used cast or forged Pistons , what was your clearance set piston to wall?

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