--------------------------------------------------------------------------------<br /><br />I wonder if anyone has any idea's.I bought a second hand mercury 500 50hp pullstart engine it had been standing for a few years but had been stored indoors.Got it home and got it started but found it was running rough,traced this to a broken wire at the switch box ,fixed this and it started first pull and idled fine. Fitted it to my boat tried it several times over the next couple of weeks while I sorted the rest of the boat out and it always started fine. Got it in the water started great, tick over was perfect ,took the boat out for a run and everything was fine for about 15 minutes then I noticed it wasn't picking up as fast as it was and didnt have quite as much go.Reduced the revs to idle and it cut out but started up first pull.Decided to head back ,got us back ok but definate lack of power. Put the ears on to flush it out and it was a real pain to start had to have the throttle half open to get it to start and it was running rough but managed to flush it out ok. Just been down to it today when I got there found the engine was siezed, freed it off quite easily fitted new plugs ,checked it had a spark but it would not start removed a plug from time to time to check if they were oiling up but they were all dry(When I took the old plugs out earlier one of them looked very slightly rusty).Checked the carbs and found both float chambers full up.Have taken the carbs off to rebuild them but have not found any blockages etc,Any suggestions?????????
<br />I'd start with a compression check.