Vintage Dirt Bike Q & A

Doing some experimental stuff with my points ignition system on my 74 cr 250 Elsinore, and think I may of burnt my coil or mag,

Can someone tell me what I should read with an Ohm meter when testing the coil and Magneto.

I cant seem to find it anywhere on any threads,

I have test the out put wireon several different magneto's that I have ( output wire = + / ground wire = -) and two of them zero the meter, and one never moves the meter off of 1.0 .

And when I test the coil from gound to positive wire it zero's the meter, then I test positive side to plug wire and it shows about 10 ohms.


Any help appreciated,

cbly

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C Bly

74 CR 250M
74 CRF 175
75 XR 75
77 ProFab Aberg HL500
97 Montesa Cota 315R
2003 CR500 AF
2004 CRF 450

I recently took some readings on my '74 CR125M ignition components. The stator 'spark' winding and ignition coil readings should be close enough to use.

You'll need a good meter - and some unusual settings - to take these readings. I have a Fluke 87 (which I consider a very good meter), and even then I had to pull out the manual to figure out how to set the meter for peak-hold and 1 mS sample time for the voltage readings. It was worth it, though, because voltage readings show actual performance rather than just wire resistance. For the coil input resistance, I shorted the leads and zeroed the meter to remove the lead resistance before taking the reading.

At any rate...

Ignition coil input resistance (red & green or blue/white & green wires) .7 ohms
Ignition coil output resistance (green wire & plug cap) 10,600 ohms (10.6k ohms)
Stator coil output resistance (red wire & ground) 275 ohms
Stator coil output voltage - approx. 140 to 160 peak AC volts when kicked over rapidly

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