How I tested my ignition coils

[Jim Bob21]

So I was out the other day and my Vk seemed to experience a power loss that happened fairly suddenly..making me think it was electrical. I checked many things and removed plugs and checked for spark etc. I read in the service manual that you need a special tool that allows you to test coil reserve capacity. The manual says my coil should produce a spark of at least .24 inches. So I came up with a way to test this without buying a special tool. Worked really well. See video. Hope it helps someone else. All tested good..I changed my plugs even though they looked good. So far so good

Yamaha coil reserve spark test

 

[Skiduty]

Thank you for posting that, I’m curious, in the test procedure that Yamaha lays out, is the spark supposed to jump 1/4” in open air as in your demonstration? Would the coil be even stronger while the engine is running? Or no, Just trying to pick up a few more tips lol. I like to tinker but don’t have a ton of experience.

 

[74Nitro]

Just a heads up on these to always make sure you use the right coils if you ever have to replace. Using the 4 cylinder coils will destroy the CDI box. Had two cases come to me where this had happened. Sometimes the aftermarket lists them wrong.
But, the original coils RARELY fail.
On another note, the newer efi yamaha sleds can test for spark without cranking the engine over. It's pretty cool.

 

[Jim Bob21]

Thank you for posting that, I’m curious, in the test procedure that Yamaha lays out, is the spark supposed to jump 1/4” in open air as in your demonstration? Would the coil be even stronger while the engine is running? Or no, Just trying to pick up a few more tips lol. I like to tinker but don’t have a ton of experience.

No it shouldn't be stronger when running. The reason being it's basically CDI ignition fired with an ignitor. The ignitor will function exactly the same with engine running or not because its powered by the battery and fired electronically. Technically there may be a slight difference when battery is charging...but usually the electronic side (ignitor) probably has it's own internal voltage controls. He older magneto driven ignition with points all ran on magneto output that did increase with rpm

 

[Jim Bob21]

Just a heads up on these to always make sure you use the right coils if you ever have to replace. Using the 4 cylinder coils will destroy the CDI box. Had two cases come to me where this had happened. Sometimes the aftermarket lists them wrong.
But, the original coils RARELY fail.
On another note, the newer efi yamaha sleds can test for spark without cranking the engine over. It's pretty cool.

Actually that's great to know and when researching I did indeed see that mentioned. Could look identical but as you say are very different