1991 Johnson 120hp V4

[Brayan01]

I have a 1991 Johnson 120hp V4 outboard engine.
Last year it worked very good, however this year I’m experiencing some problems with it.
It has 120 pressure on every cylinder. When I started it recently it works but on one of the cylinders the plug has turned black. The engine does not work properly and it shakes.
It has a new water pump .

Please let me know if you have any ideas on how to fix this. I would really appreciate your help.

Thank you,
Brayan

 

[racerone]

A black sparkplug indicates a cold running cylinder.-----Perhaps one of the carburetor floats has an issue.----Note ----Carburetors on starboard side feed the cylinders on the port side.

 

[Brayan01]

Thank you! I will start from there and keep you posted if I have any further questions, your help is much appreciated!

 

[Faztbullet]

It can also be from a ignition problem...