Evinrude 1985 8HP 2-stroke - electrical grounding issues

[BruKen]

Hi. My tender/ auxilliary motor normally is ultra reliable and gives me great peace of mind as a backup. Just lately though is will go through a period where it will just not start at all. Not even a pop. Leave it for a while and it's back to being old faithful.
I would like to get to the bottom of this. Two possible symptoms. I have noticed that before it starts acting up I often get a hell of a shock during the preceding run on startup where the coil seems to be grounding. At that point the engine still runs like clockwork but the next startup is a non event. The other possible symptom is the engine has been lying horizontal / flat either in stowage or in the car boot (i.e. will not start during the fresh water flush out after performing well at sea all day)

I have checked for obvious grounding issues but cannot see anything out of the ordinary. All leads look to be in good condition and making good contact. Both plugs get very good spark. Engine is immaculate despite it's age and only alteration from original is the wiring in of a saftey cutout lanyard inline with the engine cut-out button on the tiller arm. Where should I start troubleshooting from?

 

[Rick.]

I've found starting up the motor in the dark will show errant spark you would never see in daylight. That's where I would start after looking for obvious wire insulation breaks and nicks. Best of luck. Rick.

 

[BruKen]

Good tip, thank you

 

[BruKen]

Typically, the motor is now proving ultra reliable and starting on the first pull everytime now that I want to check it with no hint of grounding / shock either. Now what? I cant wait till I'm at sea and need an aux and hope it doesn't fail? Any other tests I could try?