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  1. #1

    785 pro not running right, wrong prop????

    Turns out I had the wrong prop guys, if anyone is interested in a solas x series prop 16.5/23 pitch, let me know. Suggested for 785 pro with engine work, or polaris 1050 or 1200. Its brand new with 1/2 hour of use on it, shoot me a pm with an offer.


    Hey guys, this is my first post, so be gentle.

    I just picked up a 1997 Polaris SLX 785 Pro yesterday.

    The Ski is in real clean condition and only has 52 hours on the hull, and 2 on the rebuilt engine.

    The engine was apparently built by a reputable dealer in michigan. The previous owner had told me he had trouble with the ski idling properly and it only did 57 MPH, so he just took it to the dealer, and they installed a new prop (solas) and put new plugs in, and adjusted the carburator, and it should now run close to 65 MPH.

    Well I went for a very short ride today, and it rode ok, but power didn't seem to be there, or atleast what i assumed it would be. It was a little sluggish getting ontop of the water, but once on the water, it moved real quick to about 50mph, then i held the throttle for probably 15-20 seconds wide open and the best I got was 52.6 MPH at 6550 RPM.

    Also, at 50+ mph, when you let of the throttle it doesn't seem to have any performance unless you open it wide open again. It sometimes stalls at idle after you slow down also, it seems to idle at 1100 ish RPM, but it seems like it would like around 1250 to me.

    Anyways, I thought I had read that these ski's like to run at 7800 RPM. Any thoughts on why mine is only running 6550. Also I am not sure what size prop the previous owner put on, what is the stock prop size.

    A buddy of mine had the same ski a few years back, and he said his would only do about 50mph, until he got the engine broke in, then eventually it would run about 68mph on the speedo

    I would like this to get out of the water in a hurry, but also do 60+ MPH if possible.

    Also what are the best bang for your buck performance add on's that I should get.

    thanks
    Last edited by soo785; 05-29-2009 at 09:08 AM.


  2. #2
    04gtxsc's Avatar
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    Not an expert by any means but does the gas gauge work. If it gets low on fuel I think they go into limp mode and limit the rpms.

  3. #3
    no, the gas guage works fine, or atleast seems to. The trim also works fine. Forgot to mention, there is a fair amount of oil laying under the engine bay and near the back of the ski, doesn't look like injection oil, more like gear oil??????????

    But there seems to be a few clear lines that lay down there, is one of them a oil injection overflow, maybe the oil was filled to high and it bleed its way out the overflow into the hull???????????

    Any help is greatly appreciated.

    thanks

  4. #4

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    check and make sure the Exhaust valves are opening ,open the seat and start it up and see if the valves open when you rev it up .

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by soo785 View Post
    ...there is a fair amount of oil laying under the engine bay and near the back of the ski, doesn't look like injection oil, more like gear oil??????????

    But there seems to be a few clear lines that lay down there, is one of them a oil injection overflow...?
    Welcome to the Hulk

    Click here for the Polaris Service Manuals.

    It sounds like you need to take the time to check everything over, and make sure things are connected and working the way they should be.

    There should not be any oil in the bottom of the hull. Clean it out, and check where every oil line goes. Check for loose clamps, cracked hoses. There is no 'overflow' oil hose.

    There is no other oil in these machines, just the 2-stroke oil from the oil tank.

    Check the oil tank to make sure it isn't leaking. Make sure the tank air vent check valve is in place, and the oil sender and filler hoses are not loose.

    Actually, now would be a good time to replace all the fuel and oil hoses in your 12 year old machine. They can fail from age.

    If the hull interior is really dirty, you can use a mixture of Simple Green and bleach to clean it up. Start with just a good dose of simple Green. Pour it in, then take it for a ride on the trailer. That will slosh it around, and help get the oil cleaned out.

    Tip the nose of the trailer up high (you can shift the hull back on the bunks to make this easier, just remember to latch the winch). Remove the drain plugs, and hose it out. Put a plastic bag over the engine air intake to prevent water from getting into the carbs.

    If there is still a lot of gunk, do it again, and maybe add some bleach. Be careful, wear old clothes, and don't breathe the bleach fumes. Having a clean hull not only makes the work area nicer, but often you can see problems that were hidden by the dirt.

    Near the back of the hull, there should be two clear hoses. One connects to the speedometer pitot nipple, under the drive shaft. The other connects to the vent nipple on the battery, if you have a regular lead-acid type battery.

  6. #6

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    Yeah, sounds alot like valves not opening to me also. Or maybe sticking/dirty valves.

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by soo785 View Post
    ...1997 Polaris SLX 785 Pro yesterday.

    The Ski is in real clean condition and only has 52 hours on the hull, and 2 on the rebuilt engine.

    ...the dealer, and they installed a new prop (solas) and put new plugs in, and adjusted the carburetor, and it should now run close to 65 MPH.

    ...a little sluggish getting on top of the water, but once on the water, it moved real quick to about 50mph, then i held the throttle for probably 15-20 seconds wide open and the best I got was 52.6 MPH at 6550 RPM.

    ...about 68mph on the speedo

    I would like this to get out of the water in a hurry...
    It sounds like there is something significantly wrong with your machine. The Pro 785 was made for strong acceleration, and what you are describing doesn't sound like the engine is producing the power.

    The speedo readings can be inaccurate, especially if the intake grate has been changed from stock. A portable GPS is the accurate method of checking speeds. On GPS, I think these models run about 60mph (GPS measured), but should get there very quickly.

    Are you sure it is firing on all three cylinders?
    What do the spark plugs look like?

    Have the carburetors been rebuilt?
    I know you said the engine was rebuilt, but that may not have included the carbs.

    I have my doubts about a shop that would simply leave a lot of oil in the bottom of the hull - that is just sloppy.

    Take the time to get this figured out. The fastest way to damage one of these engines is to keep running it with a problem. You have a very high performance 2-stroke engine, and it must be running 100% properly, or it will not last long.

  8. #8
    Quote Originally Posted by 785 lugs View Post
    check and make sure the Exhaust valves are opening ,open the seat and start it up and see if the valves open when you rev it up .

    at what rpm do the exhaust valves open????

  9. #9
    Quote Originally Posted by K447 View Post
    It sounds like there is something significantly wrong with your machine. The Pro 785 was made for strong acceleration, and what you are describing doesn't sound like the engine is producing the power.

    The speedo readings can be inaccurate, especially if the intake grate has been changed from stock. A portable GPS is the accurate method of checking speeds. On GPS, I think these models run about 60mph (GPS measured), but should get there very quickly.

    Are you sure it is firing on all three cylinders?
    What do the spark plugs look like?

    Have the carburetors been rebuilt?
    I know you said the engine was rebuilt, but that may not have included the carbs.

    I have my doubts about a shop that would simply leave a lot of oil in the bottom of the hull - that is just sloppy.

    Take the time to get this figured out. The fastest way to damage one of these engines is to keep running it with a problem. You have a very high performance 2-stroke engine, and it must be running 100% properly, or it will not last long.

    to my knowledge it was running on 3, don't think it would do 50mph on two, would it???? Should the carbs need rebuilt already, it only has 52 hrs on the unit. the motor was rebuilt last year, and the hull is very clean, so i assume the oil in the bottom is a recent issue.

    thanks

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by soo785 View Post
    ...Should the carbs need rebuilt already, it only has 52 hrs on the unit. the motor was rebuilt last year, and the hull is very clean, so i assume the oil in the bottom is a recent issue...
    Carbs can get gummed up from improper storage, and just the passage of time.

    Engine hours really don't tell you much about what the carbs are like inside.

    Is the gasoline old and stale?

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