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1980 40hp Mercury weak spark?

A

AV 25

New member
I bought a used boat and motor combo, I was told at the time the motor did not run however I have another motor and just really wanted the boat. I thought I would take a look at the motor and see why it would not run. It has 160 lb compression on both cylinders and is getting gas and seemed to have spark, but will not run, spit, pop, smoke, or do anything. I even (though I don't like doing this) tryed a shot of quick start and nothing at all. It has spark but it looks weak so I decided to try a spark tester on it with a 1/2" gap and there was no spark, so I tryed 1/4" gap and no spark, so I tryed 1/8" gap and no spark, so then I tryed less then 1/16" gap and finaly got a small tiny spark. This is on both cylinders! I checked the coils and both ohm out good with a multimeter. I even tryed two NEW coils but still have the same weak spark. I tryed running a ground wire from the stator to the switch box to each coil, but still the same problem.
I baught a Mercury repair manual that covers 2-40 HP motors from 1965-89 so I could get the readings to test the stator and trigger, but can't seem to find my motor info in it. All the 40 hp stators it lists in the manual have different color wires than mine so I don't know how to test it or what reading I should get on my mutimeter. The motor is a Mercury 1980 40 HP with Thunderbolt ignition serial# 7173629 model# 1040500.

I don't really want to go spending huge amounts of $ buying part after part trying to find the problem. Can anyone here please help??

Thanks!
 
Thanks for the info.
If the switch box was bad would it also cause the problem I'm having? I was once told that simply the CDI box would either work or not work. Is this true?
 
From what I've seen, yes. The stator makes the juice to run everything. If it's weak then nothing runs.

Jeff
 
Not silly at all. The red, orange, yellow and green ones have a pigtail in the back. The black and blue ones don't--and they are supposedly not interchangeable (per CDI).

Jeff
 
Yes when I had the coils off I cleaned those spots good. Also cleaned all contact points on the coils, switch box, wires and grounding points. But still same problem. I think I'll pick up a new stator and try that.
 
Before you buy that new stator, remove the flywheel, check the condition of the wires, and remove any oxidization from the magnets in the flywheel and the lobes on the stator.
 
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