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  1. #1
    Myself's Avatar
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    Troubleshooting Fuji 650 750 780 with no/intermittent spark

    I've got myself another stumper so I thought I'd post for future reference for anybody else. First off we need great voltage. I paralleled a good car battery with a set of jumper cables.
    Voltage......above 10.6 while cranking.............I have 11.2
    GROUNDS.....battery negative to engine/ebox & ebox to engine......0.5ohms or less..I have 0.1
    Ebox internal power
    12v on red/pur and also yellow. 0v or millivolts on orange then powers up to 12v when you crank the engine over. This is the function of the LR module. The blk/yel is for engine stop, disconnect it and check for spark to confirm stop circuit is not the issue. Tan is tied into the overtemp switch, it should read open circuit, no reading to ground.
    Stator ohms
    Charge coil...red/pur to yel...0.6 ohms.........CHECK
    Excitor coil...red/whi to grn/red....490 ohms..........CHECK
    Pulse coil...blu/red to red/whi....90 ohms.........CHECK
    Trigger....whi/yel to blk...220 ohms.......CHECK
    While disconnected no colored wires should read continuity to ground, should be open circuit. If any do read to ground that would indicate a shorted down stator.
    Ignition coils
    Primary.....blk to blk/whi....0.2-0.6 ohms..............CHECK
    Secondary......plug wire to blk ....3.3kohm or 8.3kohm including caps.........CHECK
    Now if you still haven't found the issue (I haven't on this one) then we still need to test AC voltage output of the stator while cranking. These things can ohm fine but still have a problem.
    Stator AC voltage specs
    Charge......5-6 volts
    Excitor....55-65 volts
    Pulse.....20-22 volts
    Trigger....1.2-1.5 volts
    If everything here checks out then normally I would assume the cdi is at fault.
    On this particular unit everything checks out just fine but I have an intermittent spark that reappears every 4th or 5th try and hangs out for a few revolutions before ghosting again on me. Does the same thing with a known working cdi. All the above specs are from a good running 780 with no issues. I am currently in the process of parts swapping to make sure everything checks out in the running machine.

    If anybody has any ideas throw them at me!!!


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Woodruff key. Check the flywheel.

    Really easy to do.

    Put MAG at TDC and remove the timing inspection plug. If you don't see the degree gauge, you jumped time.

  3. #3

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    bad stator even though the readings are good i've seen this happen

  4. #4
    Myself's Avatar
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    This 750 fired up and ran just fine in the ski I pulled it from. Other than filling the yard with smoke cause the crankcase was full of oil. I ran it a bit until it was cleared out, did a compression check, fired it back up, then ran it a bit the next day before pulling this engine. I have to believe it's elsewhere but if other parts swapping is a dead end I'll swap it.

  5. #5
    Myself's Avatar
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    Quote Originally Posted by xlint89 View Post
    Woodruff key. Check the flywheel.

    Really easy to do.

    Put MAG at TDC and remove the timing inspection plug. If you don't see the degree gauge, you jumped time.
    Will check it out.

  6. #6
    Myself's Avatar
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    Timing was fine. I might have found the issue, will update as soon as I know for sure.

  7. #7
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    Dead ends everywhere, I've worked on this thing all day!! When I pulled the stator I found a piece of metal stuck to the trigger, it was part of a bendix gear tooth.......no change. Went ahead and swapped the stator...no change. The coils, and 2 different cdi's all make consistent spark on the other machine.

    NOTE: Trigger must make over 1volt ac to signal the cdi to spark. Through various testing my battery got a bit weak and trigger voltage dropped to 990 millivolts and NO spark at all.

    Added an extra ground, moved the main ground, unplugged guage, unplugged trim.....same. Most of the time I get spark for a few revolutions then nothing. Odd thing is if I hold throttle 1/2 open it will hit off and run and everything seems normal from 2500rpm's up to the limiter. Under 2500 rpm's and it gets rough, about 2200 rpm's and it's like you pull the lanyard....just dies. Crank it over and NO SPARK! I'm really thinking I've got a bad ground somewhere disrupting the cdi but everything ohms fine and there's no corrosion anywhere.

  8. #8
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    Have you pulled the circuit board in your eBox to check if there is any corrosion on the back?

  9. #9
    Myself's Avatar
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    Have not pulled the board cause everything is clean inside but I will pull it just to verify.

  10. #10
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    Does seem odd you haven't found the problem. Even though the two ground wires (battery to engine and battery to eBox) ohm okay, maybe try swapping those?

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