Black spark plug..

[darin99]

I have a 1990 90 horse 3 cylinder mercury. And my motor seems to not be running right. My spark plugs on the top and bottom look normal, but my middle cylinder spark plug has a real black soot on it all over. You can wipe it off but if I start the motor on the muffs and run it for awhile it turns black again. I've switched the plugs around so that's not the problem.

I have my mixture needles set like they say on all 3 cylinders. I also ran a compression test on all 3 cylinders and they all turned out alright.

Any ideas what might be doing that? Thanks

 

[milehighboater]

Re: Black spark plug..

The mixture screws are a point in which you should start from. If this is the 3 carb model then work with that middle carb. It sounds like it is a bit rich.

 

[j_martin]

Re: Black spark plug..

Float might be a bit high on the middle carb.