Mercury 9.9 Sailmate coil arcing

[bcontento]

I have a 90's Mercury 9.9 Sailmate. I started hearing the sound of spark arcing while running it and now I can see and hear it. It's jumping between the posts in the picture. The wires and plugs are new. I have to check the plug gap but assuming they are set right, what would cause this? Is the coil likely bad or is it something else?

thanks all

 

[hardwater fisherman]

Mat not be the problem but I would start by cleaning the rusty connections.. Also it looks like the other coil has a wire attached under the large bolt .. Is that wire grounded somewhere?

 

[SteveVT]

Are both cylinders firing? Remove plug wire (with insulated puller) from one cylinder at a time while idling. Both disconnection should cause a drop in RPM. If one doesn't, that cylinder isn't firing. If so suspect bad spark plug wire or bad spark plug (even if new).

Other possibilities:
bad internal coil insulation or short
cracked coil
poor ground/dirty terminals (as mentioned)
Back EMF from source filter failure (CDI box, or bad condenser if straight magneto type)

 

[Swagonmaster]

The only time I would expect to see that is if there was a crack or something going across the top of the coil or a bad plug or wire which prevents the voltage from having a useful place to go, it's hard to contain that high a voltage.