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  1. #1
    shawndak07's Avatar
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    seadoo challenger 787 poor starting/running solved

    Good afternoon greenhulk members! I have been chasing down a hard starting and poor running problem for several months now. Changed fuel lines, fuel filter, plugs several times (they were fouling out), cleaned and rebuilt the carbs. New gas everything only seemed to make the ski run a little better but was not fixing the hard starting. Motor would just turn over. Id have to turn her over maybe 10 times to finally get it to start up. Then it would idle rough and would really take off. Lots of smoke as well. Rpms would only get to 6500. I had recently redid a seadoo ski with a 787 and when I was done it started in a click, reved to 7000 rpms and was a monster so I didn't understand what could be going on. Low and behold, one day while cranking the engine over I opened up the engine bay. I noticed the ground wire was melted a little at the end so of course I grabbed the nut, burning myself. So I cleaned off the battery terminal and wire. Still hard to start. I read online to take a jumper cable and ground the battery to another part of the engine. I did this and the engine started immediately with twice the cranking power!!! It idled amazing, revved perfectly to 7000 and have yet to foul a plug. So I immediately detached the grounds from the started and relocated to a cleaner bold on the intake manifold and attached the other ground that goes to the MPEM directly to the battery. Not sure why they wouldn't put it directly to the battery in the first place makes no sense. So just a heads up to other stumped boaters and skiers. Clean your grounds and reattach in a better location!


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by shawndak07 View Post
    .. I immediately detached the grounds from the started and relocated to a cleaner bold on the intake manifold and attached the other ground that goes to the MPEM directly to the battery. Not sure why they wouldn't put it directly to the battery in the first place makes no sense...
    I am not an expert on the Seadoo engines, but the reference ground in a watercraft is generally the engine itself. Not the battery negative post.

    The engine block is the electrical 'ground', the point from which all voltages are measured and all electrical return connections to ground flow.

    The battery negative cable is there to connect the battery negative to the engine ground, not to connect the engine to the battery ground. If the battery cable between engine and battery negative post is a poor connection then the battery is not properly grounded, but everything else would still be as long as everything else is directly linked to the engine block.

    'Grounds' connect from the engine block to other things.

    I expect that would be why the MPEM was not factory connected to battery negative.
    Last edited by K447; 04-11-2017 at 01:25 PM.

  3. #3
    shawndak07's Avatar
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    Yes that is all correct but with these engines you have to remember that they simply will not run if the battery is disconnected in any shape or form. Even an old battery can cause serious issues.

    That being said the ground wire going from the battery to the engine block was creating a ridiculous amount of resistance and perhaps at times cutting out for a moment.

    All I know is I would have intermittent no starts, poor running, and was fouling plugs on a daily! The poor grounding to the battery was the ultimate fix.

    The MPEM draws energy from the battery so i thought id give it a cleaner path..

    Quote Originally Posted by K447 View Post
    I am not an expert on the Seadoo engines, but the reference ground in a watercraft is generally the engine itself. Not the battery negative post.

    The engine block is the electrical 'ground', the point from which all voltages are measured and all electrical return connections to ground flow.

    The battery negative cable is there to connect the battery negative to the engine ground, not to connect the engine to the battery ground. If the battery cable between engine and battery negative post is a poor connection then the battery is not properly grounded, but everything else would still be as long as everything else is directly linked to the engine block.

    'Grounds' connect from the engine block to other things.

    I expect that would be why the MPEM was not factory connected to battery negative.

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