js550 engine wont turn unless plugs are removed
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  1. #1
    PWCToday Newbie
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    js550 engine wont turn unless plugs are removed

    Hello guys, warm season is around the corner and i need to get my project running. I haven't messed with it in a while but i gave up and the problem is still here. Well i bought a js550 with lots of AM performance mods. Initially it had a bad e box, but i replaced it with one from my junker and i got spark. The problem is that the starter struggles to turn the driveshaft. If i remove the plugs (less resistance without compression) it turns and so does the driveshaft, and it turns with ease. But if i return the plugs, it barely nudges. I have to bump the starter button to barely get a revolution. I replaced the starter with one that was in my junker and its a good starter, it was turning the junker's engine just before installing. I have 3 batteries which all turn my high compression js650xs so i know it isn't the battery. I'm lead to believe it is something in the engine since it turns with ease, including the driveshaft, when the plugs are removed.

    As far as i know, the previous owner poured some oil in the sparkplug sockets (without turning the machine over) "because the motor sat for a couple years, to ensure the pistons moved with ease". No i don't think that was a good idea. But i don't think it is hydrolocked because i removed the plugs and ran the starter to remove the excess oil (as you would do if you got water in the engine)

    Any ideas? Thanks a lot

  2. #2
    PWCToday.com Is My Home Away From Home john zigler's Avatar
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    Re: js550 engine wont turn unless plugs are removed

    Could be pump bearings, or wear ring binding. Could also be drive shaft bearings gone bad.

    Other possibilities, bad crank, still a weak starter, or possible still too much oil in your engine.

    I know you said you tried another starter, BUT it is still possible it is too weak to turn your engine, "IF" this motor is high compression, and the other is stock.

    Try turning the engine over with plugs out, and a rag over the plug hole, pressing hard. How much oil do you get on the rag?

    Make sure to check all grounds, make sure you are not loosing voltage to your starter.

    Next, I would separate engine and drive, to eliminate drive problems.

    Ultimately, in the end, you may have to tear into your engine to diagnose further.
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  3. #3
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    Re: js550 engine wont turn unless plugs are removed

    I turned the engine quite a bit without the plugs. I had a rag over the plugs for the majority of the time. At this point there will probably be no oil.
    Yes the junker was bone stock. Good point! Is there a way to test if the starter is running strong
    I know with a voltmeter, but how do i check the ground? With the ohms setting from the battery terminal to what?
    How do i seperate the driveshaft? Is it hard to realign the driveshaft?

    Awesome explanation and breakdown of possible issues. Thanks bud. I will post some videos of my starting-attempts after i get a couple hours of sleep. Im reglcharging the batteries and i just got off of a 14 hour shift myself Xl... thanks a lot for your time

  4. #4
    PWCToday.com Is My Home Away From Home
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    Re: js550 engine wont turn unless plugs are removed

    A few more possibilities:

    1. Starter solenoid is bad. Sufficient current cannot go through the solenoid contacts and your starter is being deprived of current. To test this, put the plugs in and short across the solenoid terminals with a screwdriver.

    2. Bad connections or bad cables. The large cables may have corrosion on the terminals. Disconnect each and clean appropriately. If you see green or dark brown on the copper portion of a cable near the crimp by the terminal then it is suspect. An ordinary resistance test is not a good way to test current carrying capacity of cables. Testing the voltage at the starter terminals (ground contact point at the engine block is often considered a starter terminal) while cranking and comparing this to the battery voltage while cranking might give a clue to this if the voltages are significantly different.

    Quite often you can diagnose a difficult-turning engine or jet pump by turning the engine over by hand. You might need to remove the coupler cover and turn it over using the coupler.

    The easiest way to separate the engine and drive is to unmount the engine from the bed plate and slide it forward. You will need to disconnect the exhaust and any cables/hoses that prevent this.
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  5. #5
    PWCToday Newbie
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    Re: js550 engine wont turn unless plugs are removed

    I bet it's the starter... the more i think of it, with this being a higher compression engine, i bet that's it. . Anyone know where i could get one for a decent price? I doubt aftermarket would bea good idea? Id just hate to invest the money to find out that the stater isn't the issue :l

  6. #6
    I dream skis
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    Re: js550 engine wont turn unless plugs are removed

    New starter and fully charged battery, you should be all set. Had good luck with sbt starters, good warranty, reasonably priced too.

  7. #7
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    Re: js550 engine wont turn unless plugs are removed

    Man thank you guys for the help.. I've checked into the SBT starters and they sound pretty good. Ultimately, can I get a second opinion on a SBT vs "OEM-used" vs "Rebuild kit"

  8. #8
    I dream skis
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    Re: js550 engine wont turn unless plugs are removed

    Do a search, the topic of starter replacement come up often.

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