TOPIC:

i recently picked up an sr650 --frame # kz650d 11331 what is the ohm for these coils --i want to use them on another bike i have --if they fit and are the same ohms.these will be going on a 1982 gs650 with 3 ohm coils --thanks

You might want to take a multimeter and actually measure the primary impedence of the primary windings. Put the leads from your mutlimeter on the lugs where power/ignition wires are connected with the meter in Ohms scale.

sorry to talk over you wired but the coil specs for my sr650 are 23k ohms

kzwolfsr wrote:

sorry to talk over you wired but the coil specs for my sr650 are 23k ohms

That's the spec for the secondary winding (spark plug side) the spec for the primary (12 volt side) is around 3 ohms.

I have a generic coil spec question. When you say that the spec is 3 ohms, is that a maximum or a minimum? I'm used to seeing specs written something like: 5.0 Volts max, or 12.0 ±0.5 volts.

The spec for resistance is in Ohms and not volts and the spec is normally not a range but a single value (for the primary resistance). Normally, what is called a 3 Ohm coil will vary some by manufacturer. The Kaw version of the 3 Ohm coil is nominally 3.2 Ohms. The Dyna version 3.8 Ohms and the Accel version is about 4.2 Ohms are work fine so there WILL be some range that is tolerable to the system. 5 Ohms coils will work but you will get a bit less spark and lower impedence coils; like 2.5 Ohms coils, will work but will run hotter and probably won't last quite as long. Lower impedence Kaw coils came from bikes (if they are KZ) with inline ballast resistors whose function was to raise resistance which when added to the primary resistance of the coil, would total about 4 Ohms. The secondary resistance will vary quite a bit by coil. Some "3 Ohm" coils will have as low as 13000 Ohms secondary resistance and this will be normal for them and others will be up over 20K Ohms; normal for them. Since there are so MANY coil variations, if you want to know if a coil will work, MEASURE ITS IMPEDENCE with primary being critical. Know what your bike should use... if it is 3 Ohms, stay in the ~ 3 to 5 Ohms range and only install a replacement AFTER measuring its impedence.

In a nut shell the coils you have will work.

wiredgeorge wrote:

The spec for resistance is in Ohms and not volts and the spec is normally not a range but a single value (for the primary resistance).

I understand the difference between voltage and resistance. I was just using a voltage spec (with a tolerance) as an example. My question addressed the lack of tolerance on the coil resistance spec. My manual states a spec of 4 ohms (I think). I plan on measuring the coils and I wanted to know what the acceptable range is. As you mentioned, there are problems if the resistance is too high, and problems if it's too low. The manual should state something like: "3.8 to 4.2 ohms", or "4.0 ±0.2 ohms".

Thanks for the info.

It's not real critical, 2.6 ohms to 4.5 ohms or so ought to work fine.
Resistance seems to increase with age(maybe that applies to people too), as most of the older 3 ohm coils I have tested were closer to 4 ohms.

My 3-ohm Accel coils all measured 3.0 ohms when new, don't know what they are now. My 2.4-ohm KZ coils still measure lower than 2.6 ohms after 25 years. I think that it's more likely that ohm-meters out there are not so accurate in that low of a range.


Points wear faster with lower resistance coils. KZ's use 4-ohm coils for points and 2.4-ohm coils for electronic ignition (which can handle the extra current). The exception seems to be the KZ1000 which also sometimes uses a ballast, so it's coils may be lower.