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73 outboard 40 hp mercury thunderbolt cylinder problem

T

tboltt

New member
Okay, so i have a 1973 40 hp mercury thunderbolt and its only firing one cylinder. When i'd put it in the water i couldn't get it over 5 mph. it sounded like it was bogging which made me think the carb needed to be rebuilt. but when it isn't under load( like just hooked up to a hose in my garage, it runs great. i have it a shop atm, but they are taking their sweet time and i'd like to know the cause and the solution to my problem.(its time for fishing). compression is good they said they had thought it might be the switch box but now they think the switch box is good. (they have barely messed with the boat) does anyone have any idea what could be causeing this? i just want to be out on the water as soon as possible!!

Thank you for your time!
 
Sounds like a bad ignition coil. (I assume this is a twin?)

Try this: Run the hell out of it, then shut it RIGHT down--do not let it idle. Pull the plugs. The one that is oily and ugly is the bad cylinder. Swap the coils and see if the problem migrates to the other cylinder. (Make a sketch of the wiring colors so you don't get confused.) If so, that's your bad coil. Seen a lot of them fail.

Jeff
 
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