Mercury 402 Intermittent problems

[trailboss77]

I have what I think is a 1973 Mercury 402 40HP. It was running good but not has started dying on me. I start it up and it runs good at fast idle, try to idle it down and put it in gear and it dies. Run up fast idle again and have to crank it over for long periods of time before it will fire. Will fire about 10 tries before it will actually run again. Last time I did manage to get it running, I ran it at full throttle back to the landing and it would cut out to the point of just over idle, then back to full throttle and back to just over idle again. Once I pulled back on the throttle it died and would not start again. Tried new plugs thinking one was fouling out but would not start. Got it back home and checked it and had no spark. This engine has been overheated and many of the wires had cracked insulation. Taped everything I could see but maybe I'm missing something?? Did not check wires between the engine and control box. Anybody have any ideas what to look for?

 

[starcraft1982]

Re: Mercury 402 Intermittent problems

Ok,this is just my opinion so take it for what its worth.If it were my motor and i wanted to keep it,I would first verify the compression in cylinders.The very next thing i would do(provided cylinders check out ok)would be to put new wiring harness on that motor.If your insulation is brittle and cracked like you say,it needs done.You MAY be able to splice new wire in there and save money,but its very time consuming and theres no guarantee you even have good wire to splice to.If you do,make sure you use good connectors and heat shrink tubing on ALL splices.After wiring is repaired/replaced,then it will be time to check spark to all cylinders w/gap tester.I know it sounds like a lot,and it kinda is,but theres really no reason to check spark to cylinders w/bad wiring,i wouldnt think.It very well could end up being a fuel delivery issue.but one sounds more like electrical to me,and even if it is fuel related,youre still going to be fighting those wires very soon.My .02 cents only!good luck.

 

[Milduff]

Re: Mercury 402 Intermittent problems

Hey, I agree with starcraft. I just rebuilt a 1972 402. Wires were very brittle, had almost the same symptoms that you describe. Sat in a barn for 30 years. I ended up putting on new stator and two new coils (they were both cracked). Re-wired everything else. Also followed the instructions on Lync n sync from this forum. Motor purrs like a kitten now. These guys really know what they are talking about.