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  1. #1

    Question Engine compression

    After changing spark plugs, adding octane boost, fuel injector cleaner, new oil and oil filter I still can't get both my rxt x's 255 to get past 5000 Rpms. What is the engine compression supposed to be at? I tried cranking it and I am getting 90 psi out of each cylinder. What should it be at? The skis run and start fine but as soon as u push it over 5000 Rpms they starts to bog. They never used to do that and one has about 30 hours on the rebuilt supercharger and the other has about 40. Any advice besides what I stated above to get these skis running smooth all the way to 8000 Rpms or close to that? Please help!

    thanks

    Jeff


  2. #2
    benGTST's Avatar
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    Need to find something they both had in common. Did you use the same gas station to fill them up? I see you used octane booster and fuel system cleaner, but that wont take water out of bad gas. Low compression could be due to cylinder wash from cranking with bad gas.
    Try adding a teaspoon of oil to the combustion cambers and see if that raises your compression.

  3. #3
    Eastside Powersports Slow 91's Avatar
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    try another compression tester first. make sure its of good quality

  4. #4
    benGTST's Avatar
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    good thinking. Make sure you have heathly batteries, all spark plugs out.

  5. #5
    wotxxxsd's Avatar
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    Cool

    Dont add oil to the cylinders before a compression test.
    If you doo then your compression results are not accurate.
    Bad gas or boost leak.
    Compression should be 125-150 in each hole.
    How many hrs on the skis?
    Also make sure your batteries are at a good charge level for an accurate compression test.

  6. #6

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    Make sure you are not using the "learner" keys. If you have 4 keys for the 2 machines, try each 1 on both machines to confirm what each does.

    Use a different compression tester-- I purchased 1 last year that would not go any higher than 90 psi-- the valve inside it was missing and did not operate correctly-- the next gauge showed a reading of 152.

    let us know what you find.

  7. #7
    Batteries are good. The other ski showed 100psi in all 3 cylinders. I have been through several tanks of gas with them running like this. One almost seems like its just getting stuck at the 5k even when its out of the water, almost like a rev limiter is on. Is there any safety or something that may cause the ski to not rev past 5k besides using a learners key? even with the learner key it supposed to go to 5500, I am definitely using the right keys. The other one revs to like 8300 when its out of the water but when the flyboard is attached it seem to have a problem getting over the 5500 and starts bogging. They both used to push the flyboard to almost 8000 rpms. Both skis have around 250 hours. The compression tester is pretty new. I will see if I can get access to another one but both skis seem really low and I am hoping to find the problem before going in the engine and having the piston rings and the head gaskets replaced. Thanks for the help guys.

  8. #8
    Boost addict hotbird's Avatar
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    what year skis? They don't have leaky intercoolers do they?

    100 PSI is low.

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  10. #9
    wotxxxsd's Avatar
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    +1 that 100 psi is low..
    I also wouldn't rev it to 8300 out of the water...

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