Spark Plugs and top of Piston Question

I bought a boat Friday. It has a 1975 Johnson 70hp engine on it. It cranks right up and idles well, but I haven't had it on the water yet. It has a fuel leak where the cover is for the carbs. I took the cover off and sure enough half a gasket. I have no idea what this gasket is called but it is half missing. I then took the spark plugs out. All three were covered in black gunk about half way across and the other half looked pretty clean. They also appeared to be damp or sort of wet. The spark plugs look to be pretty new. I took a look at the top of the piston heads and they too had black/brownish gunk on top of them. It was only on about half of cylinder 3, I could see a clear line of where gunk was and then a nice clean piston head. I really wasn't able to get a good look across cylinder 1 and 2, but what I saw was blackish/brownish gunk built up on it. Any ideas or suggestions?

Re: Spark Plugs and top of Piston Question

You must be running it on a hose. Does the engine come up to temp, or does it run cold? Fuel mixture correct, has the boat been sitting for a while? Using fresh fuel/oil mixture? There are no adjustments on your carbs. It might not hurt to do a decarb on it and clean it out.

Re: Spark Plugs and top of Piston Question

Yes, it has been sitting for a while, approx 3 years. I only ran it for a minute or two on a hose, so I'm guessing it didn't get up to temp. It does have old gas in it.

Re: Spark Plugs and top of Piston Question

I would mix up some fresh fuel/oil at 50:1 and let it run on the hose for awhile and see if it will come up to temp. A decarb would probably still be a good idea.

Re: Spark Plugs and top of Piston Question

Sorry for newbie questions, but how long should I run it to get it up to temp? How do I know when it is up to temp?

Re: Spark Plugs and top of Piston Question

It might take a few minutes, maybe 15 or so. Some engines will not come up to temp while running on a hose. Hold your hand on the cylinder head, when it's up to temp you will only be able to hold your hand on the head for a count of 3-4.