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  1. #1

    Help with compression test

    Need help with this one. New to me (one week ago) 98 gp1200. Engine and ski are very clean. Seller started it for me and seemed to run good (i didn't test ride). I got the ski home and took it to the lake this last weekend and it ran well (hard to start until warm). Trying to start it today and wont start, even with primer and starter fluid. Have spark, I can smell fuel so.... Went and rented a compression tester. I have never done a compression test before. The videos look like I should have all three plugs out for the test?? If this is the case I guess i'm doomed because the cylinders have ZERO compression. If the test is done one cylinder at a time with the plugs in they are 98, 77, 70. When I turn over the ski with all the plugs out and tester in one hole it just blows our air-fuel mixture out other plug holes. HELP..

  2. #2
    mudslanger's Avatar
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    Try it like this only remove the plug for the cylinder you are testing. So the other plugs remain in the engine with spark plug wires removed. Wile performing the test hold throttle to wide open position making sure the choke is in the off position. Spin the engine at least 6 revolutions or until the gauge stops building pressure. Post gauge readings when you have done it like this.

  3. #3
    Looks like shraeder valve in compression tester may not be working working because now i'm getting zero compression but I can feel compression coming out of cylinder. Does a regular automotive compression tester work on these things?

  4. #4
    A regular automotive one should be fine. The description above is exactly the right way to do it.

  5. #5
    I guess I’m doomed. Looks like 90, 78 and 70. I sure am glad I took the guy at his word that it had been rebuilt less than 100 hours ago. Anyone on the forums do a rebuild service where you ship your core in? I might as well buy one with the crank done too. Kills me how dishonest people are.

  6. #6
    mudslanger's Avatar
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    I do a lot of rebuilds for people in my area. But you may not be doomed. You need to make sure that compression gauge is accurate and the O ring is sealing on the spark plug hole. You should be able to plug it into an air compressor and it should read the same as the air compressor gauge. Your numbers are some what consistent. When your motor is blown you usually have 0 psi on one or two cylinders. Check that gauge first before you rebuilt that motor.

  7. #7
    Made it to the shop. The 98 has 110-120 psi so w/in specs. The issue is that the carbs are leaking into the cylinders and flooded it horribly. Needs carbs rebuilt. Have any suggestions on someone to do it? Do you know of a set that are ready to go and could be purchased and I ship my cores? I've been reading on the carb rebuild and I'm less that thrilled about trying to rebuild them. Pretty sure it is outside my skillset.

    The 01 1200r is another story - dead middle piston. Posted about it earlier today hoping for guidance.

  8. #8
    mudslanger's Avatar
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    I have had people ship me their carbs and rebuilt them and sent them back. Does the ski have a primer.

  9. #9
    @mudsanger, I tore them off and am going to go ahead and rebuild them. I started a new thread on that http://greenhulk.net/forums/showthread.php?t=286515. I read an old thread the Bill O used to put together kits for guys with specific needs on these rebuilds. Do you know if anyone is still doing that? I can order the rebuild kit but as I listed in the new thread I’m at approximately 3k feet and wondered if I should rejet with something for the altitude or leave it stock? Also, what specific carb is on the 98 gp? BN44, SBN, SBN-I??? Is there a couple trusted vendors that guys would recommend for ski parts? Thanks.

  10. #10
    I have set up a few skis for high elevation (5000’ - Crescent). I jet per factory sea level. The biggest difference you can make is to put a lower pitch impeller in. It will never run what it does at lower elevation, but runs great nonetheless. Some of the lakes around here are considerably lower (lake billy chinook is less than 2000’).


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