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Help MC19 Spark unit

Discussion in 'Honda 250cc In-line 4's' started by inchoate, May 29, 2023.

  1. inchoate

    inchoate Well-Known Member

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    When my '88 MC19 gets to around 12,500 rpm I start to hear what sounds very much like detonation. Timing and valve clearances look good, so I'm thinking maybe the spark unit. I can't track down one for an MC19 (30410-KY1-003) but there is one for an '89 (30410-KY1-701) not too far away from me. Can I use the spark unit from a '89 on an '88?
     
    inchoate, May 29, 2023
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  2. DannoXYZ

    DannoXYZ Well-Known Member

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    Sure, if pinouts match, it should be Ok.

    Need to verify AFR, very well could be case of dirty clogged carbs getting lean at high-RPMs
     
    DannoXYZ, May 29, 2023
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  3. inchoate

    inchoate Well-Known Member

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    Carbs were cleaned and rebuilt in 2021. I went ahead and bought the '89 spark unit. If that doesn't fix the problem I'll go through the carbs again.
     
    inchoate, May 29, 2023
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  4. inchoate

    inchoate Well-Known Member

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    Spark Unit.jpg

    Here's the spark unit that came with my bike. Looks like someone's been in there at some point. New unit seems to be OK but I haven't had a chance to do a proper test ride yet.
     

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    inchoate, Jun 2, 2023
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  5. inchoate

    inchoate Well-Known Member

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    I knew that was too good to be true.

    Bike starts and runs with the new spark unit but as soon as it gets to 5K is starts to misfire and doesn't want to rev.

    Back to the drawing board
     
    inchoate, Jun 2, 2023
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  6. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Dumb question I know, but plugs & leads are good?
     
    maelstrom, Jun 2, 2023
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  7. inchoate

    inchoate Well-Known Member

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    Plugs, leads and coils are all new.

    Old spark unit runs great until it gets to about 12.5K and then it gets "fizzy". New spark unit goes flat at 5k.

    Ali Express anyone?
     
    inchoate, Jun 2, 2023
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  8. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    GreyImport, Jun 2, 2023
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  9. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    I have used the Aliexpress ones in two MC-19 and they run great and have never given me any problems.
     
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    Last edited: Jun 2, 2023
    Murdo, Jun 2, 2023
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  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    maelstrom, Jun 2, 2023
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  11. inchoate

    inchoate Well-Known Member

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    Ordered one from Ali Express, so fingers crossed.

    I'll pop the original back in for the time being, 12K is enough to get me to Radwood next weekend.
     
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    inchoate, Jun 2, 2023
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