1976 Merc 85 Fired yesterday-no spark today?

[Yella dog]

I was looking at a boat with a 1976 Mercury 85 w/ Thunderbolt ignition yesterday. The owner said the batteries were dead and would have to charge them before I got there. When I arrived he was not there, but, said he left the key and to check it out and crank it. Put fresh fuel in the tank and after a couple of tries it fired up. It ran for a few seconds and I shut it off. Didn't hear any knocking or rattling. I have tried since yesterday to start it again and there is no spark at the #1 plug and only a weak yellow spark at the #2. I have taken two people over there to try to get it started, and nothing.. What happened between it running briefly and now no/minimal spark??

 

[redjmp]

Re: 1976 Merc 85 Fired yesterday-no spark today?

Bad coils.
Mercs are notorious for them( so are johnrudes)
They are intermittent and will even meter fine but under vibration they put out a weak spark or none at all.
Temperture can play havoc as well.
Also the switch box could have failed which is another common problem.

 

[Chris1956]

Re: 1976 Merc 85 Fired yesterday-no spark today?

There is a troubleshooting procedure for the ignition system at dolphinmarineservices.com or on the CDI web site. if your have the four coil ignition system, look up the ADI ignition. if you have a distributor, look for the battery-CDI ignition.