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74 mercury 850 no spark

Michaeln3162

New member
Hello and thanks
I have a 74 mercury 850.
I am having spark issues. Took the motor to the shop last year and they said the switch box was no good so I put a new cdi box and still didnt fix the issue. Motor has great compression with new ngk flat plugs. Boat will have spark when it wants to. Last week I started it 3 days in a row with no issues and now it wont start again and verified no spark. The spark is only there when it wants to be. Any ideas? wires to distributor look good and the stator on this is only for charging the battery.
 
You might have a bad trigger; try this test
Trigger-shooting_Page_2.jpg
you might also have a key or harness issue. Don't try to pull the rotor off the shaft it's molded on, check the cap for corrosion and the carbon contact in the middle.
 
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I've never removed the motor. I also replaced the harness last year as well. I also cleaned the distributor last year. I too and thinking its the distributor/trigger.
 
Is that the CDI replacement deal with the coil included?

If so, check for 12 volts at the wire powering it (white or white/red).

Jeff
 
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