25 merc cutting out

[Dru]

I have a Mercury 25 hp Sea Pro, not sure exactly what year, but i think mid 90's. The boat sat up all last hunting season and we got it out last week to go over everything (new plugs, new impeller, change lower unit oil, etc.) and everything ran fine on the water hose w/ears. I took it out on the river today and at WOT the motor keeps "cutting out". It constantly looses power and gets it right back as if I were hitting sand bars or something. Any ideas? I have no idea where to begin. Any help is much appreciated!

 

[Dru]

Re: 25 merc cutting out

oh and its not an electric start so no battery issues

 

[limacina]

Re: 25 merc cutting out

Same problem here, 1989 Merc 25 hp. Runs perfect at idle, I rebuilt the carb, new coils and plug wires. Cuts out like its dropping a cylinder at 1/3 throttle but both cylinder water jackets are the same temp, so its not fully dropping either cylinder.

 

[oldman570]

Re: 25 merc cutting out

Check the coils and plug wires along with the wires from the switch box and the ground wire for the coils for bad wire or corrided conections. Have you replaced the fuel lines to ethanol restant new lines? Is the gas new or has it sat from last year? When was the last time you rebuilt the carb and fuel pump? Any of the forementioned could be causing the problem. Start with the wires and coils then go to the rest.
Limacina yours is probly one coil breaking down or the switchbox and wires from it to the coils.
Oldman570