Spark arrestor was fine, but I just compared the two saws with the exhaust manifold off, and the one that works doesn’t leak any fuel when you run it through a cycle, but the broken one leaks a little bit around the piston ring. New piston rings maybe? Would that small leak let enough fuel escape the cylinder and prevent it from firin up?

Compression feels like it’s right when you pull the cord. I put the carb on another 290 and it ran fine. I’m usin the same fuel in both of em. I even took the fuel line and filter from the one that works and put it in the one that doesn’t run. It worked two days ago with no problems. I set down after cuttin a few trees; it wouldn’t run the next day. Makes no sense to me.