Mercury 4HP 1970 no spark

[bob-d]

Hi all,picked up a 4hp Merc one cylinder with points,which doesn’t have any spark. Not being familiar with Merc electronics, my first step was to look at the coil. How would you test with a multimeter? I am getting o resistance across the + and – poles (1K setting) and nothing from the spark plug lead to the negative terminal. I am doing it correctly? I also have a model 98 Merc-O-Tronic, but believe I need the CD adapter to check this type of coil? If so, and I pick up the adapter (55-980 CD ADAPTER) where do I hook up the leads to check?
Also I hooked the multimeter (1K setting) to the two wires coming into the coil (from the stator?) and the meter swung up and down when I turned the motor over….points then OK?
Hopefully some of the Merc guru’s out there can get me headed in the right direction.

[Anonymous]

call me 1 914 310 7086. Dave

[anotherhassel]

Ok I have one of these engines. They are not super complicated but you need to know what to look for. First off how is the wiring? Mine needed a new stator. Next thing is how does the stair look? Is the green epoxy bubbled up anywhere? Next is to check the points insulator make sure it has no cracks anywhere. If it does just to test purposes I put a piece of tape on my original between the housing and the insulator. Check for spark. If you have spark great you need a 10 dollar insulator if no spark or the stator looks bad you need the stator. What part of the country are you in? If you are close I may be able to take a look at her in person.

[anotherhassel]

Oh btw that is the phase maker ignition. The points close instead of opening to fire. Keep that in mind when you Lync and sync. On a side note these little 4s run well. Mine pushed my 10′ Jon to 9 mph with myself in it and 12.3 mph with my 14 old bro in it.

[bob-d]

Thanks all for the suggestions. Unfortunately didn’t have any 5/16" 24 bolts that the engine requires to use for my flywheel puller, so I haven’t gotten the flywheel off yet.
Great tip on the points insulator. I can only hope that its only a $10 part to get me up and running. The rest of the ignition parts for that motor are insanely expensive.

[anotherhassel]

If you look around hard enough you can find them fairly cheap. I found my stator in the original Mercury box for 100 bux. Your results may vary. Good luck.

[enrico-italy]

Hi.

in my experience, the ignition circuit of ’70-71 mercury single is a pain in the ass.

In My belgium-made single ( and twin also) Mercury, ALL the wires insulation vanished, so many short circuits came everywhere, expecially in hidden places.

My Merc 40 soon after the complete restore starts back to fail… I found the low tension wires (sealed in the stator under the flywheel) missed insulation just a bit far from where they bent when the throttle is operated, so the entire stator need to be replaced.

Also, check the thin nude copper wire on the high tension coil body … it need to be clean and OUT from the rubber coverwhen the coil is in place to ground on the cast of powerhead .

[dockbuster1]

From the look of the coil brown ? Those were replaced under warrenty in the early 70’s with green the brown coil shorted internaly however the insulators are frequentlybad even with good coils as mentioned

[bob-d]

Thanks all for the replies.
I bit the bullet and bought a new CDI stator $220, and a few used brown coils to swap out. When I receive I will do some ohm readings on all the parts and let everyone know what worked and what didn’t. Hopefully with the new parts I will finally get spark.
Bob D

[enrico-italy]

mumble mumble…. I have some doubt about the compability between a CDi stator and the old points- style flywheel and crankcase.

’70s Mercury ignition systems are famed for year-by- year difficult fit…

I hope for You all should be ok.

Let me know if it works.

[Author]

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