Mariner115HP serial 5255071 shutoff

[proudmary]

Hello,
Totally new to the boating world but recently purchased a 1986 Cobia Sportster equipped with a 1979 Mariner 115 hp inline 6 cylinder. The motor has been performing flawlessly this spring. Have had several days on the lake fishing and just enjoying the water. Yesterday I was calling it a day, pulled anchor and was cruising back to the daok at about 3/4 throttle. All at once the motor just stopped!! No noises, backfires, nothing. It was as if I had turned the key off. When I tried to restart, turning the key would not even register a click at the starter. All other electrical devices including tilt/trim worked ok. After sever tries, the starter caught and started cranking. The motor started right up and idled great. Being new, I just idled it the rest of the way to the dock and called it a day. I cannot find anything wrong. The motor started right up when I got home and flushed it. I am very perplexed that the motor would shut down with no warning whatsoever. And now my wife is having second thoughts about going out again. We have absolutely fell in love with this community and I want to make sure we're ok.
Anyboby have any suggestions?? Thanks and I appreciate the wealth of information that is on here.

 

[dobester]

Re: Mariner115HP serial 5255071 shutoff

I am no wiz at boats, but you might want to start with ignition switch and the connections. Might be just a bad connection at switch. Hope this helps, Doug

 

[proudmary]

Re: Mariner115HP serial 5255071 shutoff

Thanks dobester. I was going to check that first. I'm not sure though if I have to remove the complete control box to get at the switch wiring or if the switch can be serviced separately.

 

[Chris1956]

Re: Mariner115HP serial 5255071 shutoff

If that motor is a '79, it will have six coils and ADI ignition. If so, the switchboxes are grounded to stop the motor. Check the orange wire that runs from the quick disconnect plug to the switch boxes for failing insulation and possible grounding. Also, since the motor wouldn't crank, check the pins and socket in the quick disconnect plug/socket for corrosion, as well as the balance of the motor wiring for dirty connections and failing insulation.

New motor wiring harnesses are availible for less than $100, on the web. Shop around.

 

[proudmary]

Re: Mariner115HP serial 5255071 shutoff

I'm not sure what ADI stands for, but this motor is a CD system with one coil and 3 carbs. I really can't find an orange wire to check or test.
Right now I'm pretty baffled. Have started it at home on muffs and it starts right up. Would love to solve the problem of why it just shut down with no warning.

 

[OldMercsRule]

Re: Mariner115HP serial 5255071 shutoff

I don't know if Mariners are the same year in and year out as the Mercs but I own a distrubuter fired 1979 115 Mercury Inline, (and I see posters here usually assume a stater and six coils which I think started with the 1980 engines), and it sounds like you have the distributer fired model too. The problem you discribed sure sounds electrical, and may be multiple problems. How sound is your battery and the cables connecting to the battery? That problem, no click on the starter, (then starts after I imagine you looked at things and may have touched the connections just enough to make contact again). I would specifically look at the mercury switch that stops cranking when the powerhead is raised. As another stated look the wiring harness over carefully, and replace if you see a lot of corrosion, (look for corrosion where the harness plugs into the powerhead, (that will be on the starboard side of the engine if distributer fired, inside the engine hood if stater and multiple coil fired). Good luck JR

 

[Chris1956]

Re: Mariner115HP serial 5255071 shutoff

sorry, I had thought the '79 Merc 115HP was six coil. If you have one coil, you have the battery driven CD system. Check the red and white wires on the switchbox. The red wire is "hot" all the time. The white comes from the ignition switch is is only hot when the ignition is on. I suspect the engine harness is intermittent, although with these old motors, it could be any part of the wiring.