detonation / knock issue on 340

Start with the easy stuff first as others have said.
When you pull the spark plugs to run your compression test take some closeup pic's of the plugs and post them here. They will tell you a lot - A/F ratio, timing etc
I pulled the original plugs yesterday, ill take pics of them when I get home and run the compression testing. I'm hoping the vacuum leak at the carb base to manifold is the issue. getting a thicker gasket to try that.