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  1. #1

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    GS electrical gremlin

    97 GS 720 motor. Ran fine for about an hour on 2 different trips. Acts jsut like a srtipped rotary vale gear, but it is not. It will stumble/start adn will not actually run on it's own. I am also getting a backfire, but I think that is just a byproduct of all the fuel and irregular firing. I am thinking it's a stripped flywheel key and it's out of electrical time, well no, that wasn't it either. I read in a post somehwere about a ski that would only fire the plugs while cranking, when you let off the starter or the enigne tried to start, and the MPEM killed the starter, the plugs would not fire. It ended up as a ground issue where the ster button was copleting a circuit. I have also read where DESS posts have caused weird things too. Any input is helpfull or troubleshooting advice on the baove things. I also have a 800 motor I need to install that has a broken off oil bath fitting in the case. Any good ideas on getting that out or do I need to tear the engine down and take the case to a machine shop.


  2. #2
    96XPSS's Avatar
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    It may be your MPEM. Has the ski been jump started from a running vehicle?

  3. #3

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    nope, no jump start. It's wierd, you can see the plugs sparking while you crank it if you hold them on the head, but I can't get it to run at all with one plug out. Both look the same and have a nice spark. With both in, it will stumble and try to run, but it is surging like it is starting, but cutting off as soon as it starts and runs on it's own. I've swapped flywheels and am going to reinsert the motor in the hull. I'll try differetn DESS post and clip a new ground from the batt. to the coil and see what I get.

  4. #4
    96XPSS's Avatar
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    Make sure the pins on your front cover and top of black box aren't corroded. Check the grounding post in the black box too, and make sure it's dry.

    Try the additional ground to the engine.

    Are the plugs wet or dry when you try to start?

  5. #5

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    Plugs are wet. I would think if the carb had a problem in it, holding it wide open while cranking it like a flodded engine would get it to at least start to run, but it is no different. I've been really busy, but will get out there tomorrow and thurs night to finish putting it back together and try a few more things.

  6. #6
    canuck's Avatar
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    I got a 97 GSI as a non running project and had multiple issues to sort out.

    Mine had a similar problem to yours in that sometimes it would run fine then wouldn't even start. Turned out to be a loose hub in the center of the flywheel, it would sometimes shift about 40deg between shut down and restart. You said you changed the flywheel check the magnet positions in relation to the key way. I'm not 100% on this but I think the 580 flywheels are different. I also had a problem with the main power wires on the multi pin connector to the MPEM were not fully seating when the connector was plugged in. The female electrical connector in the wiring harness would push back into the harness and cause intermittent shut downs and stalling. I also had a bad DESS post. Someone also installed a 787 prop in the ski and I could not figure out why it was so fast but a dog out of the hole.

  7. #7

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    Tried everything, from ground wires run everywhere to new DESS post, etc. I have spark, but the motor will not run on it's own. I think its loosing spark wehn the MPEM senses the engine is starting and kills the feed to the start soleniod. I tried a new ground to the coil and the Stator as well. I'm at a loss. I guess it's the MPEM. I have a friend who can plug in to it and look arround, I'll have to have him check it out and see if it's got anything the computer can tell him. Thanks for the ideas and help.

  8. #8
    I think I understand what you're describing with how it's kicking when trying to start it. But correct me if I'm wrong here...when cranking it over, it sounds like it fires here and there right? Sounds like it wants to start but can't? If this is right, what you are describing is called flashing or ignition flash. What happens is the cylinder warms up from continuous cranking and the fuel charge being in its vapour form starts to ignite before it reaches it's optimal ignition point. So in a manner of speaking, the fuel charge begins to blow-up before the plug can jolt it into action. This is very similar to having your timing retarded too much.

    The cause of this on a properly timed engine is a combination of too much fuel charge in the cylinder and/or extremely poor grade of fuel. If you have 87 octane, and it came from a station where they don't sell a lot, hence having minimal fuel turnover (i.e. country gas stations with higher prices or just in nowhere land) the fuel sits in the tanks for huge amounts of time. With today's crap fuel if it sits for longer than a month the octane rating starts to plummit and your quality goes out the window. Try to get all of the fuel out of the tank and the lines, pick up some premium gas from some place that sells a ton of it everyday and add some stabilizer to it. The higher octane rating will have a much more controlled flashpoint and will ignite at it's proper temperature rating which is higher than the cylinder temps but lower than spark plug fire temps.

    You are right as well...the backfiring is just from excessive raw fuel built up in the exhaust. When you mentioned the plugs were wet every time you have checked them, it came to mind that my machine went through that as well. I dug into the carbs to find the needle valve lift tabs were too high and semi-flooding my engine. I would crank it over and you could see the fuel mist fly out of the cylinders very clearly and was a real chore to fire up if at all. After adjusting the lift tabs I haven't had a problem since.
    Last edited by Schwarzenegger; 07-12-2008 at 10:59 PM.

  9. #9
    96XPSS's Avatar
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    If it ends up being the MPEM I have a brand-new one for it I'll sell cheap.

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