1997 Sea Doo XP 787 wonít start
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  1. #1
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    1997 Sea Doo XP 787 wonít start

    Hi Guys, have used this forum many times, this is my first post.
    I have a 1997 Sea Doo XP with the 787 motor in it and I cannot get it to run or fire, I have run out of ideas.
    It cranks just fine, but wonít run.
    One time, thatís right ONE time, it fired a few times just to tease me and then never again!
    Did backfire one time and made me jump and blew a massive hole in the rear exhaust hose that goes from the water box across the the exhaust port.

    Here is a list of what I have done/checked so far.
    - New battery, fully charged, actually tried 2.
    - Checked all fuses, none blown.
    - Checked ground, and ran a new ground from the coil to the battery.
    - Removed, disassembled and cleaned both carbs
    - Using fresh fuel
    - Removed magneto cover to inspect and check the stator and magneto. Both looked ok and measured ok with the multimeter
    - Inspected and checked trigger coil, reads within the ohms range from the shop manual, I donít remember the actual value was
    - Checked ignition coil with multimeter, primary and secondary coils both read in spec, also replaced it with a coil from a running machine.
    - connected a test light to the white wire that I believe sends the Ďfireí signal to the coil from the MPEM, and when i crank it flashes
    - Spark tester shows that I am getting a spark
    - I can see a spark when I ground the plug when cranking
    - Tried spraying with starting fluid and on a different day also tried pouring a little gas down the carbs.
    - Fuel pump is working I added a clear line so I could see if it was flowing when I crank the engine.
    - Compression is 150 on both cylinders
    - Changed the regulator

    When the carbs were off the Rotary valve was rotating smoothly and appeared to be in the correct position when the Mag piston was TDC. Although I donít have the protractor for measuring the angle correctly.

    Someone suggested I was getting weak spark, but not sure how to test or what I should be expecting, with a spark gap tester it will only spark across a 1/8Ē gap. is that OK?

    I think that covers everything I can remember right now. I must have missed something, hopefully someone out there may be able to point me in the right direction.

    Thanks!

  2. #2
    PWCToday.com Is My Home Away From Home WFO Speedracer's Avatar
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    Re: 1997 Sea Doo XP 787 wonít start

    Here is my best guess, either the fuel is bad (I have had it happen twice on different skis) or you have completely flooded the engine, first I would remove the spark plugs and ground the wires on the the terminals provided to do so, spin it over and see what comes out of the spark plug holes, if fuel comes out it's flooded, if oil comes out the inner crankshaft seals are bad and the crank needs to be replaced, if neither of those two happen then reinstall the plugs ,hold the throttle wide open and spin it forever to see if it starts, if that does not work mix up some fresh premix, remove the flame arrestor cover and dribble a small amount into the carbs, repeat the process.
    Last edited by WFO Speedracer; 01-13-2020 at 09:10 PM.
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries

    WWSRD , What would Speed Racer do ?

  3. #3
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    Re: 1997 Sea Doo XP 787 wonít start

    Thanks, I will have give that a go and let you know what happens.

  4. #4
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    Re: 1997 Sea Doo XP 787 wonít start

    No oil or fuel coming out of the cylinders with the plugs removed.
    Still wonít fire after cranking and cranking.


    Sent from my iPhone using Tapatalk

  5. #5
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    Re: 1997 Sea Doo XP 787 wonít start

    I think that I have a bad MPEM.
    I know that it would be a lot of work, but can the 96 XP 787 electronics be spliced into this ski? looking at the wiring diagrams it looks like it is possible? maybe this unit.. http://arieltek.com.br/produto/MSD-07-98

    Or has anyone had any luck repairing the MPEM.

    Any thoughts from the experts out there.

  6. #6
    PWCToday.com Is My Home Away From Home WFO Speedracer's Avatar
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    Re: 1997 Sea Doo XP 787 wonít start

    Those are notorious for ground issues in the rear elect box, everything grounds to the bottom ignition coil mounting bolt which screws into plastic, I drill all the way through the plastic and install a 6mm allen head bolt from the back side and a nylock nut, make sure all eye connectors are clean, either by wire brushing them or by sanding them, reinstall and tighten,also check the ground wire from the battery to the rear electrical box, no ground, no fire , there are also known issues with the connectors at the top of the rear electrical box those must also be clean, if in doubt replace them with new ones, The white wire is the signal wire for the coil make sure the coil is getting a signal, check it where it plugs onto the coil.

    I doubt it's the MPEM but stay far far away from those Arieltek MPEMS, they are junk, OEM only. You can swap in a 96 setup but to do so you will need the entire 96 grey box and a 96 wiring harness.
    Last edited by WFO Speedracer; 01-17-2020 at 07:41 PM.
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries

    WWSRD , What would Speed Racer do ?

  7. #7
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    Re: 1997 Sea Doo XP 787 wonít start

    I did check and clean the grounds, and also add a extra ground line from the coil back to the battery with no luck.

  8. #8
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    Re: 1997 Sea Doo XP 787 wonít start

    I turned my attention to the MPEM the last few days, since that seems to be the only remaining thing that it could be.
    The 5A fuse slot had a 20A fuse in it, not good...
    So I began the painful process of removing the board from the case and the potting compound, more out of curiosity than anything else, and this is what I found. A trace was burnt, and when I removed and tested the MR2535L diode it was bad, open both directions when tested with a multimeter.
    This is speculation on my part, but I wonder in the Diode failed, for whatever reason, kept blowing the 5A fuse, so someone put a 20A fuse which did not blow and and caused some other more serious damage, including burning that trace/track in the board
    I did replace the diode and install a jumper to reconnect the burnt trace, without any success.
    Unfortunately regardless of how it happened, it seems that a bad MPEM is probably my issue in this case.
    It has been a fun project. But I think this is where it ends... Thank you for your help @WFO Speedracer

  9. #9
    PWCToday.com Is My Home Away From Home WFO Speedracer's Avatar
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    Re: 1997 Sea Doo XP 787 wonít start

    Yes you are correct that is exactly what happened, the 5 amp fuse protects the circuit as does the diode, once the diode blows it will immediately blow the 5 amp fuse as soon as you plug it in the MPEM , so some smart individual obviously smarter than the engineer who designed the MPEM decided to upgrade the fuse to 20 amps , this allowed it to fry the rest of the circuit inside the MPEM.

    Let me check tomorrow I may have a 97 MPEM I can sell you at a reasonable price, I do have several of those skis on the lot that I am not going to put back together.
    Last edited by WFO Speedracer; 01-23-2020 at 06:54 AM.
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries

    WWSRD , What would Speed Racer do ?

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