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  1. #1

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    Ready to give up

    I've had some problems with my '93 sl750. I found all three base gaskets were blown so I replaced every gasket in the top end and figured that would fix my problem but I took it out today and tried it.....same thing! Starts up and runs fine at low throttle but when I try to go over about half throttle it bogs down???

    A little background......Upgraded the fuel pump and replaced all fuel lines, Cleaned the carbs and went to pre-mix. I was always convinced that it was a fuel problem but now I know for sure that it is not.

    When I took it out today I had 3 brand new plugs in it, I rode it out past the no wake zone and gave it some gas and it just bogs down so I took it back to the dock and pulled the spark plugs out to see how they looked and the 2 closest to the front of the ski looked just right, then I pulled the plug out of the back cylinder and it looked brand new like I just put it in?? It never fired gas? I loaded it up went home and checked for spark and sure enough it has spark. Checked compression and had 105# started the machine with the front 2 plugs and left the back one out and it blows gas out of the plug hole??? So I have spark,fuel and compression but that cylinder won't fire?? Is there some sort of timing that could be off and only effect the 1 cylinder? Reeds maybe? I'm at a loss here and don't know where to look next.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Time to do some diagnostics...

    Check the crank shaft indexing. Service manual has the procedure.

    Connect only the rear spark plug. Will it start?

    You might need to warm it up a little first, and give it some throttle while cranking. If it starts, you have combustion in that one cylinder.

    The ignition system on your Fuji engine fires all three spark plugs together, every time any cylinder needs spark. So you can swap the plug wires around and see if the problem moves with the PTO plug wire.

    Sometimes the spark plug wire ends get frayed inside. Remove the plug boots, trim 1/4" from each spark plug wire end, and re-screw the caps onto the wires. See if that makes a difference.

    Another possibility is that there is a water leak inside and you are steam cleaning that spark plug while the engine is running.

    When running on the water, put your hand on each cylinder. They should all feel about the same temperature. Not so hot you burn your hand, but almost too warm to hold you hand there for more than a few seconds.

  3. #3
    Moderator beerdart's Avatar
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    Try swapping the plug wires and see if the problem moves to the other cylinder.

  4. #4

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    You might need to warm it up a little first, and give it some throttle while cranking. If it starts, you have combustion in that one cylinder.
    Tried that, It won't start but it will start on either one of the other cylinders.
    The ignition system on your Fuji engine fires all three spark plugs together, every time any cylinder needs spark. So you can swap the plug wires around and see if the problem moves with the PTO plug wire.
    That's nice to know I'll try it out right now
    I'll try swapping the wires around and trimming them back a little bit

  5. #5

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    I plugged the wire from the back cylinder into the middle plug and it fires right up. Tried the middle wire on the back cylinder and got nothing?

    So it's down to crankshaft indexing or a water leak? Is there something in the bottom end that could be letting water in, It has new gaskets from the cylinders up?

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    An air leak into the PTO crank area is a possibility...

    Check the crank index first.

  7. #7

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    Sounds good I'll try that tomorrow morning and report back. Thanks again

  8. #8
    la90043's Avatar
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    also if that pto plug looked brand new after the no wake zone and you rode it back. And you have spark for sure. Then that one low speed jet is plugged/clogged. take out that low speed jet and see with a magnifying glass and make sure that is the correct jet size for your ski. also the pop off pressure can be too high and cause that low speed lean condition also.

    definitely fuel problem. check that pop off and pull out that low speed jet and clean it out and then with air pressure blow it out. check that jet size too.

  9. #9

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    I'll pull the carbs off and make sure again. The cylinder is getting fuel....I left the plug out and started it with the other 2 cylinders and it blows gas out of the plug hole. Could it still be the low speed jet?

  10. #10
    la90043's Avatar
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    also make double sure that spark plug wire is all the way in and screwed on tight into the boot.


    Quote Originally Posted by rmkrider1 View Post
    I'll pull the carbs off and make sure again. The cylinder is getting fuel....I left the plug out and started it with the other 2 cylinders and it blows gas out of the plug hole. Could it still be the low speed jet?

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