I checked the plugs on the boat yesterday, and found that #1 and #3 are clean and #2 and #4 are black and sooty.

Before that, I ran the boat around the bay wide-open with the water intake slightly closed (engine is raw-water cooled but runs in fresh water). I was looking to run the boat at around 160F or so to try to clean some of the carbon out.

In general, the boat runs a bit rough and feels like it runs on 3 cylinders. However it seemed to be smoother yesterday and makes decent power, though not as much as many years ago it seems. Also after I slowed down it sounded like it had a valve tick.

I'm going to do a compression check on it soon to see if that's OK.

Any ideas on the plugs? What else could I do to clean out any carbon build-up? Run hotter plugs? Can you get a thermostat or something for the raw-water cooled engines so that they run warmer in general?

Sorry for the somehwat rambling message...