ST90 no spark...

Discussion in 'CT90, CT110, ST70, ST90 Discussion' started by Malm, Aug 13, 2018.

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  1. Malm

    Malm New Member

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    I bought a used motor to drop in my ST90 as mine is locked up.
    I installed the replacement motor.
    I installed a new battery.
    I made sure all connections were connected (that I can see, I am no expert on ST90)
    If I kick it, I get no spark...
    I get power, as the speedometer light works, neutral and high beam indicator...
    That is all that work as I have not checked any bulbs...
    No spark at all...

    Not sure where to begin to look...
    I opened the points cover and the points look ok and open as the should....

    Where to start, what to check?
     
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  3. b52bombardier1

    b52bombardier1 Well-Known Member

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    Are the points clean and properly gapped? A test lamp attached between the flat points spring and engine ground should come on and go off as the engine is rotated.

    Rick
     
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  4. Malm

    Malm New Member

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    Points look ok, gap is right, there is power, at the points, on and off as I kick it.
    Coil ohms right and rectifier checks right, according to:
    https://ct90restoration.blogspot.com/2018/06/how-to-test-your-ct90-rectifier.html
    Ground good on engine...
    No spark when kicked...

    Only thing I see that I question is, the white wire from the points, is connected to a black wire next to the main connector by the motor, is that correct?
     
  5. b52bombardier1

    b52bombardier1 Well-Known Member

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    New spark plug or old? If the white inner porcelain is black and oily, the spark dissipates across the oily film rather than sparking. The white points wire should go to the green coil wire.

    How good of a condition is the high tension spark plug wire to the plug cap? Have you checked for continuity through the plug cap?

    How many volts do you see at the flat points spring?

    Rick
     
  6. Malm

    Malm New Member

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    New Spark plug, new plug cap on end of wire, bought a new coil, but since old one checked ok, I put the new cap on and trimmed the wire to new... Coil tested good and so did under 10K ohm test from coil ground to end of plug wire. I will check voltage at points tomorrow...
     
  7. Malm

    Malm New Member

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    From this, it looks like the white wire from the points plugs into a white wire, mine has a black wire alone, and a 4 wire connector....
     

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  8. wanrep

    wanrep Active Member

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    Replace the condenser if you haven't done so.
    It's attached to the coil.

    My wiring diagram shows the same as yours.
    Black wire from the points goes to the condenser.
     

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