So I have a Briggs & Stratton Engine model number: 422437 it's a twin 18 i/c I got it for free from an older gentlemen who buys and sells lawn mowers. It's been sitting out in the weather for who knows how long before I got it. So I took it home and drain edge the oil first off and at first water came out and then oil mixed with sludge. I cleaned all that out and realized I couldn't turn the flywheel. Pretty much siezed from sitting with water in it, but I got it clear and took off all the outer metal for the air ducts so to speak and cleaned off the outside of the engine and take off the carbon and clean it all up and what not. Long story short i take off the spark plugs and find out the cylinder heads are filled with rust (no surprise there) so I take some air to it and blow most of it out and take the heads off and clean everything up to the best I can. Clean up the valves the best I can but they have some carbon build up thats caked on And one of the valve seats is loose so I put it back to where it's suppose to be and I make sure it won't move again..Try my best to clean everything up yet I notice a very obvious problem with the piston and head in one the cylinders it looks like a tiny pieces of metal got in there as it was running and left small indents on both the piston and head. As I said I clean everything going the best I can and put new oil in it and make sure the starter works and put it all back together and try to start it after all the cleaning of the entire engine inside and out. Takes a little starter fluid of course and it fires up and seems to run alright and super loud (doesn't have any exhaust besides two little pipes) and then I notice one of the cylinder heads is getting hot and the other isn't so I feel the exhaust and only one is hot. I came to the conclusion that I have a dead cylinder. Has spark (seems weak) getting fuel and is going through the motions with the help of the working cylinder. So my question is what could cause this and how can I test these possible options of issues. Any info is of help to me thanks!