Hi everyone,<br />I'm new to outboards, so have some patience please.<br />I have become the owner of a 1979 140 horse inline six mercury engine on a 16 foot boat.<br />I have been having trouble with intermittant power loss, particularly after low speed running, and a rough idle. Wide open,it runs and sounds great, but sometimes the engine just bogs and sounds "hollow", unable to accelerate past about 2000 rpm even though I advance the throttle, and I have to run at about 10 mph for a while.The engine dies if I give it too much more throttle. After a few minutes the engine starts to accelerate on its own and I can slam the throttle wide open and get instant response. as long as I keep the revs up, it will continue to run good, until I do 1 of two things:<br />1) shut down, cool down, (fish a while),and restart or <br />2)idle around for a few minutes, then attempt to accelerate.<br />"Warming up" the engine at about 2000 rpm with the fast idle lever for a few minutes before starting out seems to prevent this from happening, but I have to throttle down sometimes and it happens almost any time that I run at idle in no wake zones for a few minutes and then attempt to accelerate.<br /><br />Anyway, Ive checked for spark on all cylinders and it seems good, as does the compression (115 to 120 on all cylinders while cranking).<br />Fuel is fresh, and it does this running off the boat's built-in tank as well as a portable tank.<br />Squeezing the fuel bulb does not help the problem when it is occurring, Spark plugs are new,timing and throttle pick up settings are all to spec. etc. I've re-ajusted the idle mixture for the best idle that I can get (screws about 1 turn open). Engine did run better than when screws were 1 and a half turns open, so I thought that the plugs might be getting wet-fouled at low speed. When I pulled all the plugs out, the top 5 cylinders all looked the same, wet with fuel and a single dark mark across the insulator where the spark had been jumping, but number 6 was completely clean.I switched it with a dirty plug and ran a few minutes on the muffs, and got another clean plug, this time there was some milky white goop on it, indicating water entering the cylinder.<br />If I pull the wire off this plug while running, there is a noticeable loss of power, and the compression is good, but I am suspecting that this cylinder may be dropping intermittantly at idle, since I can't get it to idle very smooth, as I would expect from a six-cylinder engine. I don't know if this could be related to my power loss problem or not, but it sure doesn't seem good.<br /><br />I'm looking for advice from anyone who has experience with this sort of thing, and would appreciate hearing from you. I'm not altogether sure that the water in the cylinder is the cause of the acceleration problem, but it might be why I have a crappy idle and have to set it to 1000 rpm to keep it from dying when I put it in gear.<br />I'd like to fix the water problem and then try it out on the lake again.<br /><br />I am a professional auto mechanic, but I have no experience with 2-stroke water-cooled outboard engines, so I don't know what to check first as the possible entry point of the water.<br />Am I correct in assuming that the head gasket is a possible cause? I have also read some discussion about a gasket in the exhaust port area. I don't want to just start replacing gaskets if this is a common problem with a known cause.<br />By the way, is water supposed to exit the center of the prop with the exhaust, or is this a possible clue to my problem, <br />Any help would be appreciated,<br />John
