Which part of an inboard engine does a power boat exhaust puff out explosive fumes?

Im sure you read this in the owners manual or the dash, it is not as concerning as they say, however what they are talking about is the fumes that find their way from inside the engine up to the tappet covers (these are the rectangular metal cases that are on both sides of the engine above the cylinders. your tappet covers should have little hose fittings that come out of them and then these hoses should connect somehow to the air intake, assuming you have a carburerated engine. the idea being to recycle these explosive fumes back through the combustion process. if you have a leg drive, the exhaust usually comes out the end of the propeller. hope this helped.