1985 75 hp Mercury - won't rev in water

by Jacalyn Margittay
(Door County, Wisconsin)

we just bought a 1985 75hp mercury. we had the motor company where we bought it put it in the tank and all was well. we then took it to the water and started it. it runs about 1/4 throttle and then it dies out. we changed the plugs, back to the water and got the same result. we used new fuel. same thing. we checked the spark and the 2 lower were sparking but the 2 upper were not. we changed the coils. back to the water. same thing. we took it back to the motor company and they fixed a wire and put it in their tank and it ran fine. threw all the water out of their tank. we took it back to the water AGAIN and the same thing happened. anybody have any ideas?

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Sep 24, 2009
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starstarstarstarstar 		75hp wont rev under load
by: steve

I had a 75hp mariner same age and is the same as the merc. I had the same proplems, i managed to trace down to two things either the triger switch or the switch box. The two lower plugs on my engine had no spark changed triger switch but still the same. I then changed the feed wires from switch box to top two coils too the bottom two coils.The bottom two then sparked and two top didnt so the switch box wasnt powering up for two of the coils. I fitted a second hand switch box and it solved the problem.
Sep 11, 2009
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starstarstarstarstar 		1984 75 HP Merc shuts down, won't stay running
by: Anonymous

Having same problem I am, sounds like. I had my '84 75HP Merc rebuilt last year. Ran it first time last weekend. Ran solid and strong almost 2 hours, but then as we approached the ramps to unload, it start choking down like running out of gas. I still had 1/3 tank remaining! I can recrank and it will run 2-3 secs, then power down. Over and over. I'm looking online for someone that has experienced same thing so I can fix and get out on lake couple more times. Tony

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