One weak spark following the plug

[Brendan W]

So I have an old coil of unknown origin on the bench, looks to be oem. Primary measures 2.4 ohm, secondary 12k and came off a '79 misfiring points ignition machine and from the butchered wiring is not original. Spark is weak and red and only one side fires on my test rig. If I swap the plugs over the spark follows the 'good' plug. Set of new plugs, same thing. Weird. Is this a dying 4 ohm coil?

[eil]

Tell us more about your test rig. Sounds more like a loose/broken/corroded connection somewhere.

Coils rarely go bad and when they do, a resistance check tends to tell the tale. From those numbers, your coil sounds fine.

[Brendan W]

The, ahem, test rig is bolting the coil to a plate with a few long wires to break into the bike harness. I switch condensors in and out with croc clips with the old one unscrewed from the points plate. The plugs are laid on the crankcase. Found a 4.5/16k ohm coil in a friends parts bin last night.Two nice fat sparks on the rig. Replaced the condensor as well as it seemed to be intermittently sparking the points.I had tried the condensor by itself initially but no joy. Just back from a test ride over the mountain.
Like you I'm not convinced the old coil is finished. It's on the shelf.