Merc 115 87 model fouled plug

[g.reed]

Where should i start looking

Where should i start looking for the plug fouling problem. It is in the #5 cylinder and appears black with some crud buildup on it and this plug has stayed this way since i have owned the motor. all other plugs are clean. Plug wires?coil? and help is appreciated.

 

[tonyob]

"g,

You should check the sp

"g,

You should check the spark. It should jump a 7/16 inch gap. It probably will.

You should check the engine compression. Note if this cylinder is different from the others.

I think you will find some small hoses on the starboard side of the engine. They are part of the oil drain system. Sometimes a tiny orifice is clogged which causes oil to build up in one area. This oil can get burned in one or more cylinders.

Whatever the cause, I think you have carbon in the cylinder. It may pay to remove the cover over the intake ports for this cylinder and take a look at the rings. If carbon is building up there it will become a problem at some time.

"