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  1. #1
    justin1328's Avatar
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    STX-R 62 MPH @ 80 psi! Possible?

    Not really sure what is going on here... I have a 2002 STX-R, 96 hrs... Rebuilt pump, new plugs and fuel filter. The ski seems like its running great, granted my last ski was a 94 SeaDoo XP Anyway, once I rebuilt the pump and changed the fuel filter and plugs, I ran the ski for a solid 2 hours with a passager and was reaching 62 -65 mph ( 270 lbs + full tank ), smooth accelleration and top end, sounded and felt great! Decided to do a compression test tonight and I am reading 80 - 90psi with 3 different testers. First tester is 20+ years old, so I ordered a cheap digital tester from Amazon and was getting 75+ psi. 20 year old tester I am getting 80 psi, and a new tester from harbor freight is coming in at 80 - 90 psi. Threw some two stroke in to the cilinders to see if compression would go up and it made no difference. All that said, I know these skis should be coming in over a 100 psi, more like 120+. A few questions, is it possible that the readings are correct and the ski is running this well? BTW, no smoke. 2 - are these compression testers just crap and these are normal readings for these testers? 3 - If this is normal for a ski of this age, is it time for a top end rebuild? Rings, pistons......? Thank you guys in advance for your help.

  2. #2
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Are you testing with the throttle open all the way?

    Sean

  3. #3
    justin1328's Avatar
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    Yes, I did. I should have mentioned that, as I knew that would be one of the first questions from you guys..

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  5. #4
    Quote Originally Posted by justin1328 View Post
    Not really sure what is going on here... I have a 2002 STX-R, 96 hrs... Rebuilt pump, new plugs and fuel filter. The ski seems like its running great, granted my last ski was a 94 SeaDoo XP Anyway, once I rebuilt the pump and changed the fuel filter and plugs, I ran the ski for a solid 2 hours with a passager and was reaching 62 -65 mph ( 270 lbs + full tank ), smooth accelleration and top end, sounded and felt great! Decided to do a compression test tonight and I am reading 80 - 90psi with 3 different testers. First tester is 20+ years old, so I ordered a cheap digital tester from Amazon and was getting 75+ psi. 20 year old tester I am getting 80 psi, and a new tester from harbor freight is coming in at 80 - 90 psi. Threw some two stroke in to the cilinders to see if compression would go up and it made no difference. All that said, I know these skis should be coming in over a 100 psi, more like 120+. A few questions, is it possible that the readings are correct and the ski is running this well? BTW, no smoke. 2 - are these compression testers just crap and these are normal readings for these testers? 3 - If this is normal for a ski of this age, is it time for a top end rebuild? Rings, pistons......? Thank you guys in advance for your help.
    How are you checking your speed? The built in speedometer is not accurate. Install a GPS speed app for your phone and see what you are really getting.

    From what I've read stock compression should be between 110 to 130 or so. Since you tried three different compression gauges already I have to assume yours is a bit low. If it is running great and your happy with the performance then you can wait to rebuild it when you feel it is necessary.

  6. #5
    justin1328's Avatar
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    I did use a GPS app on my phone and watch and it seemed pretty consistent with the speedo... And I am getting up there a little in age, 46, so it seemed pretty dam fast to me! Seriously though, it seems like the last run I had was really good, smooth acceleration, good hole shot, good top end. Granted I am still bonding and getting to know my ski, but this is not my first rodeo, and I think I am very in tune to paying attention to the nuances of the ski. That said, it all just felt good, but these readings are throwing me a little, and if they represent a larger issue, that is my ultimate question. If a top end is in order I would like to determine it now, so I can plan for the project this winter so my ski is ready to go in the spring. Tks Beeker!

  7. #6
    Quote Originally Posted by justin1328 View Post
    I did use a GPS app on my phone and watch and it seemed pretty consistent with the speedo... And I am getting up there a little in age, 46, so it seemed pretty dam fast to me! Seriously though, it seems like the last run I had was really good, smooth acceleration, good hole shot, good top end. Granted I am still bonding and getting to know my ski, but this is not my first rodeo, and I think I am very in tune to paying attention to the nuances of the ski. That said, it all just felt good, but these readings are throwing me a little, and if they represent a larger issue, that is my ultimate question. If a top end is in order I would like to determine it now, so I can plan for the project this winter so my ski is ready to go in the spring. Tks Beeker!
    shouldn't be to hard to pull off the heads & look at the cylinders,you really don't want to mess them up,replacing can get costly.

  8. #7
    Quote Originally Posted by justin1328 View Post
    I did use a GPS app on my phone and watch and it seemed pretty consistent with the speedo... And I am getting up there a little in age, 46, so it seemed pretty dam fast to me! Seriously though, it seems like the last run I had was really good, smooth acceleration, good hole shot, good top end. Granted I am still bonding and getting to know my ski, but this is not my first rodeo, and I think I am very in tune to paying attention to the nuances of the ski. That said, it all just felt good, but these readings are throwing me a little, and if they represent a larger issue, that is my ultimate question. If a top end is in order I would like to determine it now, so I can plan for the project this winter so my ski is ready to go in the spring. Tks Beeker!
    If it is running that well and at those speeds I don't know if I would worry about it. Like kartracer said you could pull off the cylinder heads to inspect the cylinder walls and tops of the pistons. That couldn't hurt and all it would cost you is a new set of gaskets. It can be done easily in the hull.

    Are all three cylinders outputting the same PSI?

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  10. #8
    My stxr gps at 63mph, theres no way your getting 65-66mph on a stock machine that is ultra territory. The dremo meter isn't something to go by.

    The compression numbers you have are very low, but they are even. Stock machines i have always seen alittle under 120psi. Unless your gauges are all off it might be time for a top end in the near future

  11. #9
    steve45's Avatar
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    Quote Originally Posted by justin1328 View Post
    And I am getting up there a little in age, 46, so it seemed pretty dam fast to me!
    You're getting up there in age at 46??? I'm old enough to be your father, and I love the shoulder-wrenching acceleration of my 310X!


  12. #10
    justin1328's Avatar
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    Wondering if the following could explain the low readings? 1- Cold engine? Service manual states thoroughly warm up engine (98 – 155 psi usable range). 2- Compression adapter is about 1/4~ shorter than the plugs, so I know the volume is more, just not sure how many psi it would be thrown off by... I guess I could answer this myself by warming up the engine and getting the correct adapter, but I’m curious as to what you guys think.

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