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  1. #1
    Sly Fox DKFox's Avatar
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    Exclamation SPX 800 (787 engine) will not crank... what to try next?

    Hi folks. I'm new to the group. I've recently bought two older model skis. Both require some work to get going… but for $900 along with a double trailer I thought I’d give it a shot. The one I'm working on now is a 1998 SPX800 that has had a lot of mods done on it due to being a racing machine. The guy that sold it to me had rebuilt it and said it cranked fine 15 months ago before parking it. It has not been cranked or in the water since the rebuild. (He and his son race 2 stroke motorcycles and he has a garage full of those. So he knows what he is doing.)

    Problem: Engine spins just fine but it never fires up.

    So far I have done this:

    1.) I checked compression. 150 psi both cylinders.
    2.) Motor turns freely
    3.) Verified that the safety switch is a closed (shorted) circuit when the lanyard cap is placed on. (No smart switch. No buzzers.)
    4.) Brand new Odyssey battery. Spins the engine no problem.
    5.) Verified that two ground cables are on the battery.
    6.) Disposed of old gas. Pre-mix system. New 40:1 gas mixture now in tank.
    7.) New NGK spark plugs.
    8.) It gets a spark to both plugs… but appears weak to me. What is normal??
    9.) Rear electrical box components are in great condition. No build up of any kind.
    10.) Front electrical box has had an MDI brand CDI placed in it. A lot of wires look to have been snipped to put that CDI in there. However, I don’t think that is my problem since he only messed with the top end during the rebuild.
    11.) Took the Fuel Primer valve off and found out it does not work. Tried priming the carbs by putting some fuel in there and also the top of the cylinders with a little fuel.

    What next??? Verify timing but getting to the rotary valve? Or is there another ground / safety switch I need to be looking for?? Thanks for any feedback folks can give.


  2. #2

    Join Date
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    I would lean towards the weak spark issue. If the motor spins over, it is not a ground on the motor. It could be a ground in the mpem or rear box, but not likely. The timing of the rotary valve does not come into play if you poured fuel down the spark plug holes. Just a little tip: I always premix a water bottle full of fuel and keep it around to put fuel down the cylinders for safety purposes. If it cranked after they put it back together, that rules out the timing issue as well. I would look at the coil. If the skis are both 787s, you could swap coils to check it. Also, check the gap on your spark plugs. And check to make sure the store gave you the correct plugs. I have been handed the wrong plugs at Autozone and not figured it out until later in the day when I was having issues.

  3. #3
    Sly Fox DKFox's Avatar
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    I used the NGK BR9ES spark plugs and set them with a gap of .025". When you say "check the coil"... do you mean the ignition coil in the rear electrical box? What is the normal resistence I should find there? Unfortunately I bought a SeaDoo SPX800 and the other is a Polaris SL650. So I can't simply swap out coils.

    Also, I forgot to mention that the spark plug wires were just laying in the SPX800 when I got it home. I clipped the ends 1/4 inch and replaced the caps. However, I'm uncertain which plug wire goes to which plug! (ha.) The very first wire out of the electrical box (standing at the front of the ski looking at the box it would be the far right side of the electrical box) I currenlty have hooked up to the rear cylinder. Is that correct?? I tried swapping them but to no avail. I have the shop manual and no where in there could I find that information!

  4. #4

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    That ski works on a wasted spark system. That means that both spark plugs spark every time so the wires can go to either plug.

  5. #5

    Smile

    I run br8es however if it doesnt even fire when you prime your cylinders,sounds like weak spark.Normally even if your fuel to carbs is shut off and you put a bit of premix down spark plug holes or into top of carbs it should fire briefly.you should have a fat blue spark .if not perhaps coil is broking down and or mpem is on blink.And perhaps if your spark is real weak it doesnt even spark under compression,now both plugs need to be grounded when checking spark not just one,make sure your plugs are not oil fouled (fouled plugs wont fire under compression)and that plug caps test between 9-15k resistance (meter set on ohm),unplug your 6 pin mag. harness test with multi meter white wire and black/yellow wire you should get .2 to .5Vac trigger coil is bad if not.then test ignition coil between primary and secondary side it should read (set to ohms) .41 +or- .05ohms If all this fails perhaps you should look toward the modded portion of ignition,and loose or otherwise poor connections.hope this helps>Marvin ps even doo shop manual says after testing ok sometimes parts replacement is only fix!!!>Marvin

  6. #6
    96XPSS's Avatar
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    Yes, use BR8ES, as they are recommended for this ski and a hotter plug than the 9's.

    Check the pins inside the plug on top of the black box for corrosion. And the ground post inside this box.

  7. #7
    Quote Originally Posted by 96XPSS View Post
    Yes, use BR8ES, as they are recommended for this ski and a hotter plug than the 9's.

    Check the pins inside the plug on top of the black box for corrosion. And the ground post inside this box.

  8. #8
    Quote Originally Posted by Edgar800sd View Post
    SICK! ThundarCats! My favorite show as a kid! Mumra Rocks!

  9. #9
    "Tearing it up on the water" seadoobutch787's Avatar
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    i had that problem before i just un hooked the coil, wired wheeled the coil grounds and the wires and it was fine.

  10. #10
    Sly Fox DKFox's Avatar
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    I worked on this SPX yesterday and still have not been able to get it to run. I’ve done the recommended checks listed below and all appears to be normal. Bright blue spark now that I’ve been told to make certain the other lead is grounded when checking. I primed the fuel lines (installed a bubble primer) until I saw it come out of the back carb’s fuel tube which then goes back upfront into the fuel tank. I even tried spraying some starter fluid down the cylinders. The engine turns just fine but simply will not crank!

    I’ve now pulled the engine out and have it on my work table. My plans now are to make certain the carbs are clean. Will go ahead and change the grey Tempo lines out with better fuel hoses. Last I’ll verify that the timing was set correctly after the previous owners rebuild.

    Any hints on this procedure are appreciated! I just plan to follow the Timing procedure starting on page 08-02-5 of the Service Manual. I’ll use the degree wheel (pdf version) that I found here in the forums.

    Once that is done I’ll pop the engine back in and see if she cranks. If not…. My guess is I have a Gremlin that lives in the front electrical box that houses the modified MDI ignition.

    Trouble shooting suggestions are appreciated.

    SeaDooButch787: Please elaborate on your suggestion of "wired wheeled the coil grounds and the wires and it was fine". Provide detailed steps for me to follow. Thanks!!!

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