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  1. #1

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    spark plug problem

    why did this happen? started my 95 750 last week and it seamed to run rough. so today i decided to look into it before i try to put it in the water for the summer. it started again and didnot idle good
    i pulled the plugs and this what i found
    now i am not getting any spark. i looked in the plug hole and it looks like the mark of the plug on the top of the piston. how could this happen?? it does not seam to be a throwned piston couse it still moves in the cylender



  2. #2
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    Rod bearings going bad. The piston was able to come up high enough to do this. Unless you have the incorrect plug and its too long.

  3. #3

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    Quote Originally Posted by BryanP View Post
    Rod bearings going bad. The piston was able to come up high enough to do this. Unless you have the incorrect plug and its too long.

    No they are the correct plugs ....NGK BPR7ES

  4. #4

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    Quote Originally Posted by BryanP View Post
    Rod bearings going bad. The piston was able to come up high enough to do this.
    wouldnt the compression in the cylender keep preassure down on the piston so it would not do this even if the baring was bad?

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by lippyat13 View Post
    Quote Originally Posted by BryanP View Post
    Rod bearings going bad. The piston was able to come up high enough to do this.
    wouldnt the compression in the cylinder keep preassure down on the piston so it would not do this even if the bearing was bad?
    Inertia trumps compression pressure.

    The piston is moving upwards so fast that the compression cannot stop it before it hits the spark plug tip. The connecting rod and bearings are high precision and highly stressed when the engine is spinning at high RPM.

    Once the bearings have failed the piston can move upwards more than it is supposed to.

    Inspection is required to determine which end of the connecting rod has the bad bearings.

  6. #6

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    ok so there is a bad baring. what about the spark?? why would i get no spark now??

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by lippyat13 View Post
    ok so there is a bad baring. what about the spark?? why would i get no spark now??
    Did you replace the bent spark plug with a new plug?

    Lanyard in place, battery still healthy and charged?

    How are you checking for spark?

  8. #8

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    Quote Originally Posted by K447 View Post
    Quote Originally Posted by lippyat13 View Post
    ok so there is a bad baring. what about the spark?? why would i get no spark now??
    Did you replace the bent spark plug with a new plug?

    Lanyard in place, battery still healthy and charged?

    How are you checking for spark?
    i am not getting spark at any cylinder. the battery is fully charged the lanyard id on, and the plugs are new. i dont have a spark tester just doing it the old way of grounding to a head bolt

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by lippyat13 View Post
    ...
    i am not getting spark at any cylinder. the battery is fully charged the lanyard id on, and the plugs are new.

    i dont have a spark tester just doing it the old way of grounding to a head bolt
    The ignition system on the Fuji engines is generally robust. The CDI just needs all the wiring connections to be good, especially ground, the ignition coils, and of course the stator.

    Sometimes more than one problem can happen at the same time, or close to the same time.

    If you want to diagnose the no-spark problem before digging into the mechanical engine, start by checking every wire connection for looseness or corrosion. The terminal board and everything inside the electrical box should be free of rust and corrosion.

    Disconnect the stator wires and do the ohm checks per the diagnostics.

    Also check the ignition coils ohms and spark plug wires.

  10. #10
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    Quote Originally Posted by K447 View Post
    Disconnect the stator wires and do the ohm checks per the diagnostics.

    Also check the ignition coils ohms and spark plug wires.
    ...

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