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  • What Happened?

    I have a Polaris sl750 with a new sbt motor. I had some prok f/a's and a jetlyne water box put on by the shop that put my new motor in. The ski use to hit 49 - 50. But now I can barely hit 45. What happened? They said to bring it back so they can adjust the carbs but they should have already done that. I mean that is what I paid them for!

  • #2
    If your max RPMs are the same as before, and nothing else has changed, then you either have pump damage, or your speedo is off (I assume you are just going by the speedo). If your max RPMs are indeed low, then they have incorrectly adjusted your carbs. Unless they are ON the water testing the boat, they have NOT tuned your carbs whatsoever - it can not be done out of the water or in a tank.

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    • #3
      Lenchmob,
      Did you break it in yet? It should be running extra oil for the first tank of gas. The carbs will have to be dialed in precisely once broken in and the extra oil in the first tank is run through. What was your max rpm? The SL750 is around 6200. Actually, you shouldn't be running max rpm anyway until the first tank of gas is run through and the ski properly broken in. Water conditions can vary your speed too. Was it perfectly flat or choppy? I think a little more detail is necessary on your part so we get the whole picture.

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      • #4
        Sorry guys. The motor has already been broken in. The motor is about 6 months old. I hope you are not saying to break in again? The conditions were the same as I always ride. I just cant see how putting f/a's and a waterbox would make it slower. Bryan said something about pump damage. Is he talking about the prop? I went for 48-50 to 45. That is going by the speedo on the ski.

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        • #5
          You need to tell us what your Max RPMs are - there is no other way for us to know if you are reaching the correct engine speed or not.

          And PLEASE verify that this happened right after the mods, or not.

          [ March 27, 2001: Message edited by: Bryan Glynn - SBT Webmaster ]

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          • #6
            Lenchmob,
            If the reciept does not say you paid for a lake tune, you did not pay that shop to adjust your carbs. You paid them to install parts. Now you need to tune the motor.
            Bill O'Neal WCM
            <a href="http://www.watercraftmagic.com" target="_blank">www.watercraftmagic.com</a>

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            • #7
              It sounds like the engine was fine before but then the parts were added and it didn't perform well after that. Lenchmob, describe in detail what was done to your ski as stated on your invoice. Max rpm reading would be good to know too. With the speeds you posted, you should not be turning more than 6000. Did you by any chance get a top loader intake grate? That will put you exactly where you described on a stock SL750. It is not necessarily due to actual speed loss, but in the pressure that builds up to send to your speedo. You can also have debri or something in the speedo sensor? Give me all the details you can even if it is minor. Some people think that an intake grate swap is insicnificant, but in this case can explain everything.

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              • #8
                new motor dude. Dont hammer it. you need to break it in by varying speeds so the rings can seat. your compression wil build back up as the rings seat. Give it a little time. Also youre adding oil to the gas, besides the oil injection right? if you are thats good. But youre running a lot of oil. As for the carb adjustments they can only do a basic adjustment in a shop or a tank. I never tank tune my skis. You gotta go out there and fine tune them. The shop can only get you close to what it should be
                Rob

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                • #9
                  Okay. Here it is. My ski was completely stock with a new sbt motor which has alraedy been broken in. The ski used to hit 48-50. Then i put a r&d intake grate on it and had prok f/a's and jetlyne waterbox put on. They did water test cause the shop has a boat ramp and the ski had salt water on it when I picked it up. I never checked the rpm's when I rode it. Now I wished I had. When I rode it over the weekend I could barely hit 45 on almost glass on the river. I know the intake grate slows it down on glass but I thought the f/a's and waterbox would make up for it. It does seem to have a lil more low end grunt but by going by the speedo it is slower on the top end. The plugs look good because I checked them after riding it. I did not let it idle before checking them so I could get a good reading. Should I take it back to them or is this how it should be? Or should I ride it again and open the highs a lil? When I ride it again i will check the rpms out. Any info will help. Thanks

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                  • #10
                    With the design of the Polaris speedo pickup, you can have a big difference in readings just by changing your intake grate. You cannot say one way or the other if you have speed if you are just using the speedo as a gauge - forget it exists, basically. Get a GPS, borrow one, or get radared. Then switch back to the stock plate and you will see #1, how much speed difference there really is, and #2, how far off it throws your dream-o-meter reading.

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                    • #11
                      The dream o meter is the only thing I have to go by. I have no access to a gps or a radar gun. But I will put the stock intake back on and see what happens. So are you saying the r&d intake grate messes up the speedo? I know that the speedos are not the most accurate things. Just like the guys with the gprs that say they are going 70. Yeah right.

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                      • #12
                        They can be nortoriously inaccurate, sometimes as much as +/- (usually+) 30%.

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                        • #13
                          That still does not answer my question. Does the R&d intake grate mess up the speedo reading?

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                          • #14
                            Oh, sorry - yes, it will change the reading.

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                            • #15
                              Like I said about 6 posts up. If you are running an R&D intake grate, it will slow you down a little in actual speed, but the speedo will read much lower because of the pump pressure being different with the R&D. Put your stock grate back on and your speedo will jump higher. The Polaris speedo for the SL750 is actually very accurate as long as the intake grate is left stock. I gpsed my SL750 countless times and with the stock grate or even an Ocean Pro open bar grate it was almost dead on with the gps. With an R&D grate, it showed 3mph less than the gps. I am still curious as to what your max rpm is. Post it after you ride next. Just a note, the R&D actually gives fairly accurate speedo readings with the 4" extended pumps. I was using that combination as well and then my speedo was right near my gps readings. Once again though, the pump pressure is different with the 4" extended pump and seems to be well suited for an R&D grate.

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