merc 140 no spark

[cmillerarizona]

Thanks to all on this board, it seems to be packed full of good information. I have a 1979 merc 140 hp with thunderbolt ignition, and I have no spark, I read through some of the info on Cdi`s site and came across a "no fire at all" troubleshooting guide. A portion of this guide said I MUST have at least 9.5 volts on the white and red terminals while cranking, I checked and have only about 8.3 volts while cranking. Will this prevent me from having spark?, the motor seems to still turn over fast. My thought now is why did they ever include a pull rope because you cant pull it as fast as the battery is turning it over.

 

[CharlieB]

Re: merc 140 no spark

Is it a low battery, poor cable connections causing the low voltage?

Or the starter dragging and drawing the battery voltage down?

Pull ropes do not use ANY battery, so a low battery at 10V should still have fire with the pull starter where hitting the key to use the electric start would drop the voltage too low and no spark.

Check the condition of your battery, clean ALL battery cables, BOTH ends, and retest.

Maybe take that starter apart, clean the commutator, lube the bushings.

 

[Chris1956]

Re: merc 140 no spark

Cleanup the battery cables well and make sure the battery is good and well charged. Low votage at the switchbox will make for eratic operation.

You can try to pull start the motor, but I have found that to be impossible, even when I was a young stud. You can check spark by removing the spark plugs, installing them into their plug wire boots, taping them together and grounding them to the block. Now the motor will spin fast and you will have +12V at the switchbox. Use a timing light to see if you have spark.

 

[cmillerarizona]

Re: merc 140 no spark

I have been charging the battery and now I have about 9.3 volts while cranking, is that still too low for the switch box not to function, also my stator only has 2 wires coming from it so my guess is it only charges the battery while running and has nothing to do with spark unless pull starting.???