Mercruiser 120hp starting / running problems.

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broompisces
Posts: 156
Joined: Tue Feb 17, 2009 8:20 pm
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Location: Glasgow, Scotland

Mercruiser 120hp starting / running problems.

Post by broompisces »

Hello!
I'm asking for some pointers here...
I have a 1968 Mercruiser 120hp engine.
A few days ago it wouldn't start as well as it normally does. It will fire up no problem, but when you take the ignition key off the "start" position, the engine dies. This will happen 6 - 10 times until it will stay running. I am sure it is an electrical problem as it doesn't splutter, it just dies instantly - as though you've switched it off using the key.
On my last run out on it, I was proceeding nicely at 3,000 revs when it just died - no "death throes" - it just died instantly. A turn of the key, and it fired up fine again and off I went.
I've checked the fuel supply - looked in the carb. and all ok there - the symptoms do not seem fuel related to me. I replaced the "Lucas" car coil with a Quicksilver marine one in the hope that might have solved it - it hasn't.
I replaced the distributor 5 or so years ago with an electronic ignition distributor - I've carefully cleaned the dissy cap contacts inside using fine sand paper and that has made no difference.
I'm now thinking a wire on the ignition barrel may be loose - the barrel is on the Mercontrol, so it's no easy task to check it - i'll need to strip the Mercontrol box, but that's probably my next port of call. I've checked all other wires and all terminals etc seem fine.
Anyone out there got any pointers for me?
Many thanks in anticipation.
Ian.

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floater
Posts: 1065
Joined: Fri Feb 06, 2009 6:47 pm
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Location: Southern England

Re: Mercruiser 120hp starting / running problems.

Post by floater »

Ian
I'm affraid I'm not familiar with mercruiser inboards however my suspicions immediately fall on the wiring in the mercontrol box. They are typicaly pretty cramped and grubby inside and the loom is rubber insulated with a tendency to crumble. You say that you intend to look there next and I think that is where you will find the problem.
Good luck

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