Exhaust issue Cat 3306

I have a Cat 235 excavator with a 3306 Cat. I have excessive black smoke issues and realize what could possibly be going on there with fuel injectors , air intake etc. The main issue I have is the smoke is coming out of the head below the exhaust ports. I just installed new exhaust gaskets but the smoke appears to be coming from ports where the gasket just covers the square port. Normally ports would be covered with the gasket and the manifold bolted to cover and hold. There are no manifold bolts or manifold that covers those ports.