3L rough idle, one black spark plug

[boatdude100]

First cylinder plug is black, rest are good,
Hard starting after it has been run...

Has visually maybe... too big a plug gap? cant find my gap tool and will check when I get one however....
What is the most likely cause of this please?

New to me boat. Hopefully not cruel to me boat! lol
Any thoughts?
Thank you!

 

[alldodge]

Always start a motor problem with a motor serial number

One black plug could be low compression. Valve not closing correctly or rings broke. Do a compression test to find out

 

[boatdude100]

Finally stopped raining so did compression test .. all good!
Black plugs on cyl 1&4.
Spark good, Anyone know how I should proceed?

 

[Grub54891]

Tune up. Plugs, wires, cap, and rotor.

 

[alldodge]

Finally stopped raining so did compression test .. all good!
Black plugs on cyl 1&4.
Spark good, Anyone know how I should proceed?

What were the compression numbers

 

[boatdude100]

cyl 1 (black plug) 170
cyl 2 tan 165
cyl 3 tan 160
cyl 4 (black plug) 165

Now asking myself if I am looking at fuel fouling or oil fouling...? Thin black non-glossy coating on the entire tip and it gets that way within 5 min of running

 

[alldodge]

Need a better gauge, the numbers are high (150 for new motor) but difference between cylinders is good

With 2 and 3 being tan (good color), 1 and 4 is from oil. If it was fuel all would be black

 

[boatdude100]

Yiikes, thanks great perspective! So the implication is that maybe it's running rich or something?
Any idea what to check/replace next?

 

[Scott Danforth]

Could be leaking valve seals

 

[boatdude100]

If I was to add that the boat seems to run between 175 -180 deg could this help point in a direction? (besides changing the impeller this morning)

New to me boat...

 

[Scott Danforth]

If I was to add that the boat seems to run between 175 -180 deg could this help point in a direction? (besides changing the impeller this morning)

New to me boat...

Do all the maintenance that the prior owner didn't do

 

[alldodge]

If I was to add that the boat seems to run between 175 -180 deg could this help point in a direction? (besides changing the impeller this morning)

New to me boat...

Without knowing which 3L it is (ah no serial number)

If gauge is accurate its your running hot, not over heating but unless its closed cooled it's running hot