mercury mariner 150 engine trouble?

I have a 1989 mercury mariner 150 outboard (V6 w/ carb) on a 18ft boat. Freshwater only. I have only had the boat and motor for about six months.
I had a cylinder firing issue and a mercury dealer replaced the engine switch box (part# 32-778A12). The boat ran ok the next time out after that, but I am still having problems with idling. I can never seem to get the idle set right. Inconsistent acceleration and power, I removed the spark plugs yesterday. The plugs were new, I put them in shortly after I got the motor and they only had about 5 - 7 hours of total run time on them. Five of the six plugs had oil on them and they all looked pretty black.

The weird thing about this motor is one time out it will run and sound great 42-44 mph @ 5700 rpm, the next time out I hit the accelerator and the motor boggs down and dies.

Any advice, help, thoughts would be greatly appreciated!!!

Re: mercury mariner 150 engine trouble?

Re: mercury mariner 150 engine trouble?

Thank you very much,

Yes, the one plug was dry and very clean, maybe just a little black on the outside. The other plugs having oil on them (wet) that is normal or ok ?

Thanks for the other tips on wiring and the coils, sounds like that may be my trouble.

Re: mercury mariner 150 engine trouble?

bbull70, I think I'm having the same problem with my motor as you are. Mine will run fine, the after turning it off and starting it back up a few minutes later, it will not let me rev it over 1400rpm with the gears engaged. Then, I'll turn it off and restart it and after a few tries, it will start working perfectly again. It won't stutter or stall at all once it's working, but after shutting it down and restarting, it might stop working again..

Did you ever get a solution to your problem? What ended up being the problem?

Thanks,
Curtis