Coil swaps

I'm still up in the air about coughing up for a Dyna set up for this old bike, when I still have 2.5 sets of good factory coils. I checked out Zedder to see which year/models were capable of using each others coils. So it looks like you can (generally) swap KZ 650 coils from 77-80, KZ 1000 coils from 73-78, Kz 400 coils from 74-80 (400/440's), you can also use 76-80 750 twin coils on the 400's and vise versa. There may be the odd model that doesn't fit these swaps, but the lists appeared fairly comprehensive. The reason for looking this stuff up was that I saw Yamaha xs 650 replacement coils at a surprising price on a Yam site. Apparently the factory xs 650 coils are notorious for being weak and there are several new replacement items currently available at surprisingly low prices. These looked like Kaw coils and may be applicable to the 750 twins. So.....has anyone swaped coils from Yamaha, Suzuki, Honda onto their Kaws?

I'm using a coil from a 79 650SR on my 80 750 twin, does that count?

Generally what you've got is correct - you can mix and match most of the coils from bikes with points setups. The nominal primary resistance is about 3.8 ohm. Some of the bikes (honda), seem to run higher resistance coils - closer to 5 ohm than 4 ohm although these too would work.

What you can't do is use the later coils from CDI / electronic ignitions - these tend to be too low on the resistance (1.5 to 2.2 ohm) and would run hot.

I've been using a coil from a '90 GSXR 1100 for the last 20K Miles, works just fine don't know about the heat problem Jeff is refering to but then again I've never checked it. had to do a bit of wiring redo as the new coil was an externally grounded coil, thus had 2 wires one positive and one negative wire. instead of the stock one wire. hope you find a coil that will work.

Wolfman@SparksAmerica wrote:

I've been using a coil from a '90 GSXR 1100 for the last 20K Miles, works just fine don't know about the heat problem Jeff is refering to but then again I've never checked it. had to do a bit of wiring redo as the new coil was an externally grounded coil, thus had 2 wires one positive and one negative wire. instead of the stock one wire. hope you find a coil that will work.

I'm really confused, every coil I have seen has a positive and negative terminal, and I have never seen a coil that requires a ground.

steel, most of the new bikes have externally grounded coils, they recive there ground or trigger from the Ignitor box.

I'm always looking to learn something new, but I don't understand what you are saying.
My current understanding of the dual tower KZ coils:

Primary side- 1 wire to positive (+12 volts) and one (ground/negative) wire to points/ignitor
Secondary side- spark plug wire attached to each end of secondary windings.

If you are talking about a dual tower coil, I can't see where an external ground could be connected.
If you are talking about a single tower coil, then I could understand another ground wire, but not on a dual tower wasted spark system.

If you happen to have a schematic that you could post, I think that would help.

Post edited by: steell, at: 2005/11/16 09:02