Thread subject: Whaler Central - Boston Whaler Boat Information and Photos :: Mercury 90 4-stroke (carbs) fouling plug
Posted by swist on 09/04/13 - 6:16 AM
#1
Symptoms - intermittent rough idle getting worse over time, eventually leading to obviously running on 3 cyls all the time.. Tried new gas, changed all filters. Pulled plugs, all look OK except #2 is full of soot and there is a drop of gas sitting in the plug gap. Change plug, runs beautifully for a week and then problem starts again (slowly). I have hauled the boat for the season and it is in the shop but would still like to follow up on second opinions. These engines are famous for carb problems with very small passages, but in this case, all I can think of in that direction is some carb fault which is pumping too much gas or a way-too-rich mixture into that cylinder. Possible?
But is not the problem more likely possibly weak or intermittent ignition on cylinder 2? Eventually fouling the plug? I'm getting feedback that ignition problems are unusual on that model But obviously anyhing can happen. Wiring is solid and looks almost brand new. Coil?
500 hrs
Thanks
Posted by brooks89 on 09/04/13 - 7:27 AM
#2
Swap the coil with one on another cylinder and see if the problem moves to new cylinder.
Posted by awayland on 09/04/13 - 8:20 AM
#3
Do a compression test 1st.
Posted by Scott Blake on 09/04/13 - 9:40 AM
#4
Are you using any gas additives? I had problems with naphtha fouling my plugs, it was a 4-stroke yammie.
Posted by swist on 09/04/13 - 10:05 AM
#5
On mechanics advice Quickleen and Stabil (the blue kind). Has worked well - this is a 2005 engine.
On swapping coils - we'll keep that on the list but since it takes a while to notice the problem that's a lengthy procedure.
And it's in the shop, don't the Merc mechanics have things to test coils with?