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Help! SP125 Suzuki, Spark at LOW RPM only!

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I have a 1982 Suzuki SP125 ($40 piece of junk) dual sport motorcycle that I'm attempting to turn into a scrambler.

Yesterday after extensive carb cleaning, I managed to fire it up. It ran great for about 5 minutes and then mysteriously died.

I've tried the basics:

  1. Ensured the carb is clean and it's getting fuel.
  2. Replaced the sparkplug
  3. Replaced the coil etc.

It would start for a second and die, so I decided to put a drill on the flywheel and see how the spark changed with speed.

At low RPM it produces a strong spark, but when I speed the drill up the spark completely stops.

I suspected the CDI box, but other thumpertalk forums stated that it almost never "half dies" thus eliminating that from the bucket list.


Could the pickup-coil be causing something like this?

Does anybody else have this motorcycle?

Does it require the battery to run? and if so, why was it running so well for 5 minutes without a battery?

How does the key-system which runs wires into the generator case shut off the spark?


Thanks so much in advance! I'm so stumped with this one...

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So, I managed to download a manual for a DR100 which had the Ohm values for testing the CDI, Pickup Coil, Main Coil, Starter Coil. Turns out that the CDI was bad.. Kinda hard to believe it, but it was HALF FUNCTIONING! Replaced it with a Honda XR100R CDI and it worked like a charm!

I guess most SP125, DR100, DR125 of that era had BAD CDIs! They cost $300 new. Don't waste your time. Any Honda XR80/100 CDI will work or just get a chinese eBay CDI and that'll work too...


Anyways hope this helps somebody.

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I imagine the plugs don't from the XR don't work with the SP, did you cut the wires to swap out the CDI's?  

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I bought a 1982 sp125 . 900 miles sat for for thirty years . Pretty bike garage kept .

Has fuel ,spark , and air .  But you kickit and it only runs for 5 seconds  or a few pops then nothing.  Tried different carb , same result .  Flywheel is lined up, fresh gas cleaned carb , stock 38 pilot, exauhst pipe is clear, wiring looks emaculant.

It fires up first kick then nothing.

Spark is hard to see unless at night.

I have a cdi on order ...any other experiance with this?

I'll return with results.....


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