Mercury 1985 75hp ran fine, then wouldn't start

creol

Cadet
Joined
Aug 9, 2012
Messages
24
Summary: Ran fine for 1hr. After sitting for 1hr wouldn't start. Most likely electrics-related.

This happened last November. We left in the morning for a short day trip in semi-cloudy weather, temp was around 10 degrees Celsius (that's 50 F).
After running for 1hr at near idle/half throttle speeds we stopped to have lunch at a restaurant.
The engine sat for maybe 1hr, and after that didn't start - didn't even cough once. Was cranking normally but didn't ignite. Before that, cold-started and ran normally the same morning, idled properly, water was circulating normally etc. Just a couple months before that incident I had done a compression check on it, came out 123psi worst cyl, 131psi best.

I'm 99% sure this problem is not gasoline related, since there was plenty of gas in tank, vent was open and the primer was hard. The battery is quite new and had good voltage. I happened to have a set of spare plugs on board, tried to start with those as well but made no difference. We ended up leaving the boat where it died to be towed away later.

Next morning I went to the boat to try and start again - no luck. So I think that rules out the case of vapor lock (not sure if that's even a relevant issue in our chilly climate).
I've been told to sink it and buy a Yamaha, but I think this one has still several years of life ahead, since the hours are quite low (I know the history of the engine well). Makes me think of installing a kicker motor as backup, though.

So, before going around outboard salvage yards searching for expensive electrical components, could some of you guys give me some directions where to troubleshoot first. I own both Seloc and Clymer manuals for this outboard but haven't really gotten much out of them. I'm familiar with the basic tools, voltage meter etc...
Technical background: I've changed the impeller on this, plus normal carb cleaning, also tore down the power trim electric motor a couple of years ago (had sucked in water) - managed to revive that one, too.

Iboats is a great community, I've learned a lot from here, so I think the best I can do for the community is to make this a great troubleshooting story, hopefully with a happy ending.

EDIT: Okay, I had totally forgot I already started a thread on this right after it happened last autumn. But I will be posting results here.
 
Last edited:

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,033
Re: Mercury 1985 75hp ran fine, then wouldn't start

Check to see if spark will jump a gap of 7/16" first.
 

creol

Cadet
Joined
Aug 9, 2012
Messages
24
Re: Mercury 1985 75hp ran fine, then wouldn't start

Okay, did nothing but spark test and then she fired up normally and idled perfectly on the hose. I still would like to have some ideas on what to check, just to avoid this problem coming up again...
 
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