Mid 80s Mariner 50 hp with black spark plug at 3rd cylinder

[gtcwasson]

I have a mid 80s Mariner 50 hp Outboard. It wasn't getting spark at the 3 cylinder and the spark plug was black when I removed it. I put a new spark plug in and the same thing happened 'no spark' and black after running for a short period of time. I put in a new coil and got spark. But still the motor ran like it was missing. pulled #3 cylinder plug and it was black again. Any ideas?

 

[fastjeff]

See if the plug end of the wire and the metal clip that grabs the plug are installed correctly.

Jeff

 

[racerone]

Perhaps the cylinder is running cold due to other problems.----Start with a compresssion test.

 

[gtcwasson]

I have a mid 80s Mariner 50 hp Outboard. It wasn't getting spark at the 3 cylinder and the spark plug was black when I removed it. I put a new spark plug in and the same thing happened 'no spark' and black after running for a short period of time. I put in a new coil and got spark. But still the motor ran like it was missing. pulled #3 cylinder plug and it was black again. Any ideas?

I compression tested and get 119-121 in all 4 cylinders. Thanks for all your help. What is a drop cylinder test? Plugs are new.

 

[racerone]

You remove one sparkplug lead at a time while motor is idling.-------Sound of the motor should change as you remove and re-install plug lead.

 

[gtcwasson]

You remove one sparkplug lead at a time while motor is idling.-------Sound of the motor should change as you remove and re-install plug lead.

What sound am I looking for? What does that test show?