Today, I put in a replacement exhaust elbow on my 1991 Hunter Vision 32's Yanmar (1200 hours). The small but mysterious amount of white smoke that I started noticing in the spring is gone. More importantly, I'm getting the full rpms that the engine is supposed to have. Since I bought the boat used from an absentee owner, I didn't realize that 2700 max indicated a problem - I thought something was wrong with the tach. It was only last month, though, that suddenly it wouldn't take more throttle past 1800 and I knew I had a problem. I checked the fuel, filters, lines, checked the lift pump diaphragm, backed off each injector while running to make sure each cylinder was actually firing. From reading other articles I decided to pull and inspect the elbow. I used Steve Dion's post in the Photo Forum as a guide. It was easy to get the exhaust riser w/attached elbow out of the boat (closing seawater intake valve first, of course). The elbow was blocked badly on the output side. After removing a few chunks of carbonized crud, I realized that the septum that separates the water from the exhaust was also crumbling - the elbow needed to be replaced or I would risk sending water back into the engine. I gave up trying to unscrew the elbow from the fitting that joins it to the exhaust riser, and used a hacksaw to cut it away where the elbow joins the fitting. I was able to detach the old fitting from the exhaust riser using a pipe wrench and WD-40. After the replacement elbow and fitting came in at the dealer, I installed as in Steve Dion's post. By the way, the reverse (lefthand) threads are on the part of the fitting that screws into the elbow. The part of the fitting that attaches to the riser has righthand threads...