I was given an old runabout with a 1972 Johnson 100hp Hydroelectric V4. The boat had been stored for about 4-6 years without being run. It was reported to run fine when last put it in the water. <br /><br />I have done the following work to date:<br /><br />1) Replaced water pump impeller;<br />2) Checked compression (1-115, 2-115, 3-114, 4-114);<br />3) Cleaned plugs (they looked like new "surface gap" Champions);<br />3) New tank and all new fuel/vac lines;<br />4) Replaced fuel pump (old one leaked on priming);<br />5) Rebuilt carbs (upper was clean, lower was badly varnished);<br />6) Decarbed using Seafoam;<br />7) Changed the oil in the lower unit;<br /><br />I've had the boat in the water a couple of times and run it a fair amount on muffs with the same behavior. It starts easily and runs well at idle when cold. After running for 15 minutes or so, it won't idle (dies) and get progressivly more difficult to start until it finally won't restart at all. Once it cools down, it restarts fine.<br /><br />I suspect that oil fouling of the plugs may be partially responsible for the problem. After running all four plugs will have wet oil and some carbon built up on them. <br /><br />I also think I have a slight water leak into the Number 3 cylinder. I don't have the typical "clean plug" seen with water leaks, but when I removed the spark plugs immediately following the decarb job, I noticed what I believe to be steam coming from the Number 3 spark plug hole. The other three cylinders did not exhibit this behavior. <br /><br />Obviously I need to find and fix the water leak. Hopefully this is just a head gasket, but what else should I check? <br /><br />Will the water leak cause the behavior described?<br /><br />Thanks in advance for your help.
