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Thread: 250sx spark dies

  1. #1
    Join Date
    Apr 2023
    Location
    Florida Panhandle
    --
    10

    250sx spark dies

    Got a somewhat unique issue and wondering if anyone has seen something similar.

    1985 250SX gets spark for about 10 revolutions and then the spark dies. It is pretty abrupt. Strong blue spark and then nothing.

    The history is that the trike was sitting for years and I just brought it back. It was running when it was parked, but then sat too long in the rain. I had the motor out and bored it. I OHMed out everything at the CDI and it all looks good. I swapped the coil and have the same issue. I have a CDI that i am going to try, but i have to make a pigtail to mate the 1985 round pug to the two part CDI plug that seems to be so much more common. I am questioning the pulse generator and that is my next piece to swap.

    Any thoughts?

  2. #2
    Join Date
    Jul 2019
    Location
    Shelton
    --
    96
    Does it fire up and run for 10 seconds or just has visible spark for 10 seconds and you have not tried to run it yet? The pulse coil ohms out ok? The fact that you get spark means at least for an instant, everything is good. Make sure you have a good clean ground. You may be stuck with the dreaded swap parts one at a time with known good parts and see what solves it. Does that have a neutral switch? Make sure you ohm it out if it does. Usually electrical stuff breaks down when it gets hot, but you're doesn't seem to spark long enough to get hot.

  3. #3
    Join Date
    Apr 2023
    Location
    Florida Panhandle
    --
    10
    Thanks for the reply. It would run for a second or two and I would get a hot spark for a second or two. I agree that a bad ground is a likely culprit. I had the bike completely disassembled and changed the battery, key switch, coil, starter relay, piston and rings...so there was lots of things that had been unplugged and messed with. I ohmed all the grounds, as well as the coil and pulser and stator. I even pulled the left case off to make sure the pulse looked good and that water hadn't snuck in. The only thing left was the CDI. I didn't think it was likely because the trike was supposedly running before it sat for a decade. CDIs that plug into the 1985 250SX are really hard to find and really expensive. I got a cheap one from Ebay and spliced the new style connector to the old bike. There is a great thread by ps2fixer with a pinout chart for multiple years. After all that I got no spark... I happen to have a junk 1994 TRX250 and I tried that as a shot in the dark. It fired right up and ran like a champ.
    Lesson learned: CDIs go bad.

  4. #4
    Join Date
    Mar 2023
    Location
    Earth
    --
    78
    Quote Originally Posted by SoFarKingSlow View Post
    Thanks for the reply. It would run for a second or two and I would get a hot spark for a second or two. I agree that a bad ground is a likely culprit. I had the bike completely disassembled and changed the battery, key switch, coil, starter relay, piston and rings...so there was lots of things that had been unplugged and messed with. I ohmed all the grounds, as well as the coil and pulser and stator. I even pulled the left case off to make sure the pulse looked good and that water hadn't snuck in. The only thing left was the CDI. I didn't think it was likely because the trike was supposedly running before it sat for a decade. CDIs that plug into the 1985 250SX are really hard to find and really expensive. I got a cheap one from Ebay and spliced the new style connector to the old bike. There is a great thread by ps2fixer with a pinout chart for multiple years. After all that I got no spark... I happen to have a junk 1994 TRX250 and I tried that as a shot in the dark. It fired right up and ran like a champ.
    Lesson learned: CDIs go bad.
    There's no true trst for a cdi other than plugging in a KNOWN good cdi. No matter what any book or post says. They can read fine and still be bad.

  5. #5
    Join Date
    Apr 2023
    Location
    Florida Panhandle
    --
    10
    Quote Originally Posted by Shad Owe View Post
    There's no true trst for a cdi other than plugging in a KNOWN good cdi. No matter what any book or post says. They can read fine and still be bad.
    True statement. I tried a replacement Amazon CDI that didn't work first, if I hadn't had an old TRX250 module to plug in, I would have lost my mind chasing down the problem.

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