1974 Merc 115 tower of power died on water and cranks but won't start - no spark

jimijam

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Jul 7, 2017
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I'm looking for any direction as I start to diagnose this, i've read tons of great posts and plan to follow the direction. I just bought a boat with a 1974 merc 1150 (serial # 3945671) on it. I mistakenly didn't test it because I trusted the seller. He claimed it ran like new. Well it did for about 10 minutes. I was smooth and quite and idled great. After a bit At near WOT the motor completely died in an instant. It easily restarted and ran well for another few minutes then cut out instantly again. After getting it home I came to find that I have no spark in all 6 cylinders. All cylinders had 125-130 psi compression (happy to see that).

Now I'm chasing the no spark. I started taking things off to test the switch box and came across something weird (i think?). The main wire that heads from the distributor to the coil, or into the red thing in front of the coil was very loose inside. (i'm new to these older motors) It pulled out very easily, being a cylinder type pace of metal I'm assuming it's supposed to clip onto something, the way a plug wire grabs a spark plug. Should there be a post in the red thing? Any insight of guidance would be greatly appreciated. I can't get a picture to load so it's my profile picture. Thanks so much, I'm very excited to get back on the water.
 

Chris1956

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Joined
Mar 25, 2004
Messages
28,571
Mercs of that vintage can have a red color coil. The wire from the distributor cap is a friction fit into the coil. All high tension wires screw into the distributor cap.

There is an ign test for your motor on the CDI Electronics web site. It will test the coil, wiring and switchbox. If it gives spark, the assumption is that the trigger is bad.
 

jimijam

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Jul 7, 2017
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Thanks, should there be a post inside the coil that the wire friction fits over? Or does it just insert into a hollow hole?
 

jimijam

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Jul 7, 2017
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Well so I was chasing wires and making sure all my connections were good. They looked good and I was getting 12+ feeding into my switch box the whole time but somewhere in my messing around I got my spark back!

Just a question for a novice outboard guy, after the boat is running, could a loose wire to the battery kill the engine?
 

Chris1956

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Mar 25, 2004
Messages
28,571
Yes. a loose wire will interrupt power to the switchbox and kill spark. Other loose wires can damage the ign system. Clean them all up and make 'em tight.

The high tension wire from the distributor cap to the coil, fits into the hole and has friction to the coil connector.
 
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