Re: Testing coils in 1974 25 HP Evinrude

[Don]

quote Steve D:

Ok thanks Fleetwin, I tried that and did get a reading out of one around 14-15 on the 1,000 scale. And on the other coil something I’ve never seen when testing coils…the needle was actually fluctuating back and forth. I had the red lead poked right into the plug wire making direct contact, and the black lead steady on the ground terminal, and it fluctuated randomly between 15 and 50.

Could a bad driver coil damage the coils?

On a side note, I am leaving for a couple days on a fishing trip and wanted to use this motor but it didn’t run quite right. I replaced the points, condensers, rebuilt the carb but the coils were the only thing I didn’t have but suspected they might be bad. I had the universal coils on hand and so I converted this over.

I’ll have to pick up the conversation when I get back in a few days. Thanks for the help guys.

OK, that reading sounds normal. I wouldn’t poke through those wires to check the resistance though. Like I say, those plug/boot/terminals are notoriously lousy connections. The spring terminals get rusty, and the little pin loses contact with the coil wire. I would go ahead and cut the leads back (just past where you poked them-unless you poked them way back towards the coil) and replace the boot terminals. I’m thinking there is nothing wrong with those coils, unless it is burned through/arcing like the one pictured! Your meter may have been fluctuating because of a weak meter ground connection on the coil ground lead. Clean up the ground terminal, have an assistant help if needed. Keep in mind that holding the two meter leads with you fingers on them might show a reading in the range of 50,000 ohms.
I don’t really think a bad driver coil could damage the coils, but surely ANYTHING is possible when it comes to electricity, so I would never say never. The driver coil has been update/improved on these engines since yours was made, so it might be worth replacing it even if it tests OK.
I’m assuming this in NOT an electric start engine. The one thing that could damage the coils is inadvertently using the stop circuit leads as grounds for 12 volt accessories on a remote electric start boat harness.
PS- what was the original problem that caused you to convert to universal mag? No spark, weak spark? Another problem area for the low tension system is a chafed/grounded primary harness under the mag plate. These leads are constantly flexing/twisting and can be damaged easily.