Vintage Dirt Bike Q & A

Has points ignition...

Lost spark.

Checked and switched out ignition coils. No spark. Coils seemed OK.

Checked grounding...No spark

Changed condensor ....no spark

By passed kill switch...no spark..

Cleaned points and set gap....no spark

Seems no broken wires..

The only thing left to check is the alternator..But I am not sure how to check or what the readings should be.

Can anyone help?

Thanks

Try disconnecting the cable from the alternator, and using the red wire from the alternator source (spark) coil, take a resistance reading from there to stator ground, with a piece of paper / plastic / etc. between the points. The CR125M is about 270 ohms, and the CR250M should be in the same ballpark (200 to 500 ohms, give or take).

If your reading was within range, switch your meter to AC volts and kick the motor over, watching the meter carefully. You really should use a very good meter with sample/hold and narrow pulse capability for an accurate reading, but if not, just look for a reading of any kind (try DC volts too). The CR125M puts out about 140 to 160 VAC peak.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric