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No spark in 70 40hp

B

bucki

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"I just bought a 1970 Mercury

"I just bought a 1970 Mercury 40 horsepower. It is my first boat. Once I got it started it ran fine for about 30 minutes. After that it died suddenly and hasn't started since. I am getting nos spark in the plugs. I changed them, replaced all the suspicous looking wiring from the plugs back to the battery. Still nothing. It has 2 coils that I don't think would suddenly die at the same time can they?"
 
"I'll offer very little ad

"I'll offer very little advise since that engine is older than I work on. Look for the wire that grounds out the ign system, black/yellow on newer models, disconnect that at the switch box or magneto if equipped. Check for spark. These engines require no external power for starting, remove harness and check for spark also. This link might help, should be about the same for 1970
http://www.boatpartstore.com/page20.asp"
 
Thanks for your help. I discon

Thanks for your help. I disconnected the yellow wire going into the switch box and nothing happened. I then disconnected a series of three wires at the next switch and the engine fired and seemed to run fine. The only problem was that I couldn't turn it off. I had to choke it off. Now what does all that mean?
 
Why does a bad rectifier which

Why does a bad rectifier which I understand to be part of the battery charging system prohibit the motor from starting? And why does the engine start with the rectifier disconnected? When I was replacing bad wiring on this thing I noticed that one of the rectifier posts turned along with the nut. I tightened it down some and just moved on thinking that it didn't have anything to do with getting spark to the plugs.
 
"Joseph, you are right, the re

"Joseph, you are right, the rectifier would not have affected the ignition. I would suspect that what you disconnected was probably wiring that went to a key switch, neutral safety switch or the like (something heading to the main wiring harness).

It was probably one of the switches that quit on you and grounded the spark from your ignition system. Removing the wire "opened" a circuit and allowed the current to ultimately flow to the coils instead of grounding on the head...

It is time to grab a manual and have a good look at the wiring diagram..."
 
"All depends on how the stator

"All depends on how the stator is set up. 2 piece as in 1 stator and 1 charge stator, or 1 whole stator, if it shorts it could melt into the other, or something like that."
 
"JB, that's makes total se

"JB, that's makes total sense
"
 
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