Charging system and Coils questions

[powellskier]

I own a 1980 CB750 that has had some charging system problems. The magneto/rotor is measuring 1-2 OHMs. Should I replace it?

I am also looking at replacing the stock coils and possibly some wiring as well. Should I use 3 OHM or 5 OHM coils? What is the difference between 3 OHM and 5 OHM? I remember reading somewhere that the 3 OHM coils have a tendency to burn out (or something to that effect) and that running 5 OHM coils is safer for the electrical system.

Apologies in advance if these questions have been answered before.

 

[amc49]

The norm is 3 ohm and UNDER 3 ohm, I have never heard of a 5 ohm coil. The OEM ones are 3 ohm. Under 3 WILL burn the ignitors out in short order.

Your rotor is dead (internal short) by that measurement if it is accurate. Common on these, 80% of the charging issues are bad rotors. If run long enough that will wreck the voltage regulator next.

 

[powellskier]

Thank you for the input and advice. I bought a set of Dynatec DC1-1 coils which are 5 OHM coils that were used on SOHC points systems.

The rotor readings were the same on two multi-meters, analog and digital...

 

[amc49]

Rotor look for like 4.4 ohm and it really can mean nothing as the resistance can be fine and the part still be bad. The wires inside can work fine until centrifugal force makes them move slightly at speed to short out. Then slow down to a lower rpm and the bike is again charging. BTDT.