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  1. #1
    monza406's Avatar
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    new to me 2000 Pro 785 starts/idles great, but will not rev-new to this site HELP

    I just picked up a 2000 Polaris Pro 785. The previous owner stated that he started it up for the first time after winterizing it, and it started/idled fine, but would just bog each time he hit the throttle.

    I disassembled the carbs, cleaned them, blew them out with compressed air, installed new internal filters, and replaced the stock fuel lines with good quality 1/4" blue line.

    I put the carbs back together, and re-installed them with new reed cage gaskets.

    I finished everything up yesterday, installed a new battery, pumped out any old fuel, cleaned out the water separator, put in 3 gal of fresh 91 non-ethanol with 3.2oz per gallon of premix in the tank. I hooked a holley electric pump on the fuel line, and pumped about a half gallon through, just to make sure fresh premix was at the carbs.

    I installed new plugs, and fired the ski up. It started great, so I switched on the hose attachment, and it idles just fine. As soon as I give it throttle, it bogs, each and every time I squeeze the trigger. I tried choking it a bit, but that still will not allow the ski to rev.

    I noticed that the ski has a Hot Seat head on it, and no temp sending unit. I have a service manual, and it looks like the schematic shows a tan wire inside the black box that goes to the temp sensor. I unplugged that, and it made no difference.

    I am pretty sure that there are some electrical issues going on with the ski, but not sure where to start.

    The multi function display seems to be on all of the time. When I run the ski, the fuel level, clock, etc. all seem to work properly, but no rpm shows up on the mfd. It just shows zero. I unscrewed the bar pad, and disconnected the mfd, and started the ski--same thing--it will not rev up. The power trim has continuous power as well, and works, even with the teather disconnected.

    I tested the power valve servo motor, per the manual, and it opens/closes the valves nice and smooth.

    I got online, and looked up the part number for the cdi, and it shows a polaris part 3240367.

    I opened the black electrical box on the ski, and the cdi is a Mitsubishi part 17520121, with some other numbers after it--F8T34374, Igniter 78Z99.

    I did notice that there is a solid grey wire, with tiny black dashes on it, coming out of the cdi box, but the end is not plugged into the board anywhere.

    Not sure where to go from here, as I am not the best at trouble shooting electrical parts, but I am really leaning toward some type of electrical glitch limiting the rpm's of the machine.

    Any help from the Pro 785 guru's out there would be greatly appreciated.

    --Monza406


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome

    Lets start with the no RPM on the display. Trace the a Yellow and Red/Purple stator wires. Red/Purple stator wire should have battery voltage and be connected to other Red/Purple wires. Yellow is the RPM signal and also provides battery charging control via the LR module.

    Yellow stator wire should measure full battery voltage when engine is not running. It will have a weird AC signal when the engine is running. Yellow wire from the MFD display should connect with the stator Yellow wire, and also a Yellow wire from the LR voltage regulator module.

    The MFD display will enter sleep mode active minutes of no activity. It will always show the clock while sleeping. The clock display does not run down the battery.

    See my signature links for lots of info including more details on how the MFD display works.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Are you sure all cylinders are firing, and the ignition timing is correct?

    Try running the engine with only one spark plug connected. The engine should run (roughly, of course) with each individual spark plug firing. Does this first with only the MAG spark plug. Then only the center spark plug. And finally with only the PTO spark plug.

    If it does not start/run on a specific single cylinder, there is a problem. You may need to hold the throttle open a little to get it to run with only one cylinder firing.

    If it runs equally (badly) on each cylinder, verify the baseline flywheel timing. Remove the inspection port and rotate the engine (by hand) to MAG piston at TDC (spark plugs out). The zero degree flywheel timing mark should appear.

  4. #4
    monza406's Avatar
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    Thanks for the info, and here is what I found, so far:

    The yellow wire to the mfd, stator, and regulator are plugged into connecting blades on the board inside the black box. The battery measures 12.37 volts, and the yellow stator wire measures 10.37 volts when the engine is not running. When running, the yellow wire still shows 10.37 volts. The red/purple wires are connected on blades inside the box, and measure 12.37 volts when the engine is not running.

    I pulled the plug wires, one at a time, and it seems to have spark on all three. I pulled the plugs, put them in the plug boots, on the head, and they all had crisp spark when I cranked it over.

    The multi function display does go into sleep mode after 5 minutes or so. I did not realize that the oil/fuel levels, and clock show all of the time.

  5. #5
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    Have you done a compression test?

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  7. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by monza406 View Post
    Thanks for the info, and here is what I found, so far:

    The yellow wire to the mfd, stator, and regulator are plugged into connecting blades on the board inside the black box. The battery measures 12.37 volts, and the yellow stator wire measures 10.37 volts when the engine is not running.

    When running, the yellow wire still shows 10.37 volts. The red/purple wires are connected on blades inside the box, and measure 12.37 volts when the engine is not running.

    I pulled the plug wires, one at a time, and it seems to have spark on all three. I pulled the plugs, put them in the plug boots, on the head, and they all had crisp spark when I cranked it over.

    The multi function display does go into sleep mode after 5 minutes or so. I did not realize that the oil/fuel levels, and clock show all of the time.
    All the Yellow wires are plugged into the same linked cluster of tabs, labeled YEL on the terminal board, correct?

    No other wire colors should be connected to the YEL terminal group.

    Where does the Red/Purple stator wire connect?

    Something is is wrong since the stator Yellow is measuring below battery voltage, and below the voltage on Red/Purple.

  8. #7
    monza406's Avatar
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    Yes,

    Compression was excellent, at 149/148/150.

  9. #8
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    There are three yellow wires, all attached to the same linked cluster of tabs, and no others connected to that cluster.

    There are 5 red/purple wires, all attached to the same linked cluster of tabs, and that cluster is attached to a fuse, with a solid red coming off of a tab on the other side of the fuse. It looks like one is from the cdi, one is from the breaker reset, one is from the regulator, one must be from the stator, and I did not trace the other.

    I just double checked, and the battery is at 12.41 at the terminals. The yellow cluster is at 10.41--always two volts less. If I fire the machine up, and measure the voltage at the battery terminals, it does not appear to be charging, as it shows 12.2 with the machine running.

  10. #9

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    the cdi is correct as far as the rpm's not registering it sounds like your lr module is bad . I don't think it's an ignition problem it sounds carb related to me make sure your fuel on off switch is clear they tend to swell up after time and stop partially flowing fuel as far as the grey wire goes that's the wire that puts the ski in limp more and without the temp sensor hooked up that will happen so leave the grey wire disconnected

  11. #10
    monza406's Avatar
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    I will double check the fuel switch, but I put a holley electric pump on the main fuel line, to pump out any old fuel in the tank, and it pulled it through without any resistance, so I am pretty sure that is ok. I had the carbs apart, and everything looked nice and clean. I pulled the needles/seats, main/idle jets, and everything was spotless. Could bad fuel pump diaphrams on the end two carbs keep it from reving? No holes, and they were not all dry/brittle, and I replaced all of the grey line with new 1/4" blue line, and zip tied all of the hoses. When I choke it, while the ski is running, it quickly loads up with fuel, so it seems like it is getting plenty.

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