noise above 4000rpms

[shredh20]

Hello I just boughta boat with a 2008 suzuki 200hp four stroke. The boat ran great when I bought it. Two months later I ran it today and when it gets around 4000 rpms it starts making a noise like a spark knock. The noise is coming from motor not lower unit. It will continue to gain rpms but it seems down on power and noise gets worse. Below 4000 rpms motor performs flawlessly. Could it be old gas in the tank? Thanks

[boats.net]

Start with a compression and leak down test on engine.

[jemako3]

What did you find out? My motor is doing the same thing.