I recently acquired a cub cadet zero turn with a Kawasaki fr691v. It has lived its whole life outside. It’s a 2012 model. It had been sitting for three years because it stopped moving according to the previous owner. Turns out the transmission belt was bad. After replacing the belt i drove it around and heard a metallic rattling noise. It turns out one cylinder had one bent pushrod and both pushrods had come off of the rockers. This cylinder had a large lump of grass packed into it. The cylinder definitely overheated and caused an issue. Anyway i got a used cylinder head and cleaned everything up and replaced it. I actually ended up cleaning both cylinder heads and lapped the valves. I ran a compression test on the cylinders and both are right under 100psi which is good according to the manual. I adjusted the valves and the engine fires right up but at full throttle it smoke’s horribly. It has 3 year old gas in it but i mixed in some fresh. I did not touch the carburetor. It seems to run really well. The previous owner did not mention any engine issues. I don’t think he realized there was an issue as it ran pretty decently on one cylinder. The engine has a little under 350 hours on it. I am not sure what to try next. My fear is the one cylinder hasn’t been working for a long time and has been washed with fuel and now the piston rings and bore are shot but I don’t want to jump to any conclusions yet as the cylinder looked visually pretty good to me. Also on the bad cylinder the intake valve where it seats was eaten away terrible say .005-.010. Also noticed when i took the valve cover off that it was milky inside. The other valve cover had normal black engine oil.