Re: 18HP saga continues. Can’t get past 14mph and 3,900 RPM.

[mikesea]

Just some thoughts I hope it might help you out. What oil are you using? Sure sounds like it gets tight under load could it be in the tower or prop gears starting to tighten up? Outside high humidity will show up on your intake just you you are showing in the picture.
Does it use a lot of gasoline? It does not have to use a lot more gas if the mixture is very rich. What color is the smoke coming out of the engine? Black or Blue? You started with good rings and pistons a couple of times now it sure sounds like you have washed the cylinder walls down with excess raw gasoline causing the scuffing the pistons. This is very easy to do and can happen in just a very few minutes of running time. This has happened to me once a long time ago and have seen it since really many times. Many times it came back to a bad carb. By the time the fuel wash carb problem was fixed the engine had highly polished cylinders in the upper ring travel. Cross hatch LOOKS perfect but feeling it ….was a smooth as GLASS. Or If overheating in the combustion space, this will cause the pistons to over expand and the cause of the scuffing and low rpm. Three different power heads? Same tower?
One more thought is there anyway the port timing could be off?