Ignitions coils techo question

[greenman43]

Here's one from the Department of Stupid Questions: I'm trying to work out how I can put a set of cheap replacement coils on the Mk II (I have a set of
7mm Mallory leads I'd like to use, so thinking I'll pick up a set of coils from a 90s bike of some sort).

I'm completely out of my depth as far as this kind of stuff goes; put a multimeter across the primary circuit in the coils presently on the bike (no idea if they're OEM or not, but they do have the collet-type lead attachments) and got 3.8-4.1 Ohm. Wasn't able to measure the secondaries, leads / caps as they're possibly fkd. Also measured a pair of GPz9 coils tonight, which came in at 3.1-3.2 Ohms.

If memory serves, it's the ratio between the primary and secondary windings that dictate the 'output' of the coil, so I guess if the Mk II coil secondaries are roughly 4/3 that of the GPz, they'd be the same. Am I right in thinking this ?

Second point, what is to stop me installing, say, the GPz coils onto the Mk II ? I've read on another forum a comment about ballast resistors being needed, but I really don't understand any of this ...

In the perfect world I'd get a set of Accel or Dyna coils and hum off into the sunset, but my budget is pretty tight at the moment - just want to get the fackin engine actually running !

Thanks in advance,
Brian

[mick12]

sounds like 3ohm coils if you need cheap go to the wreckers and take your meter with you dynas in oz will set you back about $200 contact sirteck ( i think thats how its spelled )in Brisbane they can point you to the right ones and give you a price

[oldman]

Unfortunately it's not so simple. What you are reading on your ohm meter is resistance, what you need to know about a coil is it's impedance as they are quite different. Impedance is the oposition to alternating current flow. You cannot measure impedance with an ohm meter. If you get it wrong you could be spending a lot more than money on a coil. Impedance is the opposition to fluctuating current flow caused by the build up and collapse of the magnetic field created by that current flow. Sorry I wish it was more simple. (Pulsating DC acts the same as AC [almost]). You have a couple of, (younger) engineers in this forum whose memory is not addled by long term use of alcoholic beverages that can probably explain it better than me. Cheers!

[greenman43]

Thanks very much guys, sage advice. Sounds very much like something I shouldn't fool with - best I save my pennies until I can afford some proper aftermarket stuff (or at least, suitable replacements for OEM).

Cheers,
Brian

PS No shame in having a memory utterly trashed by ... ummmm .... I forget ...