I noticed black smoke when I increased the throttle (engine bogs). It was obvious that the exhaust elbow had carboned up - this elbow is truly an atrocious design. Since I've seen this on several Yanmar's I've owned, I thought I'd pass along a cheap, quick and long term fix.
It takes less than 15 minutes to remove the exhaust manifold with the elbow. Just undo the 4 bolts holding the manifold to the engine.
Put it in a vice (or between 2 logs like I did) and remove the exhaust elbow and the short stainless joiner piece. Go to any plumbing store (or Home Depot) and buy (Schedule 40) 1 1/2 inch NPT (national pipe thread) a 3 inch nipple, a 90 elbow, a 2 inch nipple, a 90 elbow, a 6 inch pipe threaded at at least one end.
About 4 inches down on that 6 inch piece, drill and tap a 1/2 inch nipple (for the water injection).
Into the exhaust manifold, screw in the 3 inch nipple, then the 90, then the 2 inch nipple, then a 90 and then the 6 inch section. Now you have a new exhaust elbow for under $30-.
I go to a motorcycle shop and get some exhaust wrap for the heat but I have gone months without that.
My engine has 1392 hours (hour meter was installed a year after boat was launched so maybe 50hrs more) and previous owners have replaced that Yanmar elbow at least twice at over $400-each.
It takes less than 15 minutes to remove the exhaust manifold with the elbow. Just undo the 4 bolts holding the manifold to the engine.
Put it in a vice (or between 2 logs like I did) and remove the exhaust elbow and the short stainless joiner piece. Go to any plumbing store (or Home Depot) and buy (Schedule 40) 1 1/2 inch NPT (national pipe thread) a 3 inch nipple, a 90 elbow, a 2 inch nipple, a 90 elbow, a 6 inch pipe threaded at at least one end.
About 4 inches down on that 6 inch piece, drill and tap a 1/2 inch nipple (for the water injection).
Into the exhaust manifold, screw in the 3 inch nipple, then the 90, then the 2 inch nipple, then a 90 and then the 6 inch section. Now you have a new exhaust elbow for under $30-.
I go to a motorcycle shop and get some exhaust wrap for the heat but I have gone months without that.
My engine has 1392 hours (hour meter was installed a year after boat was launched so maybe 50hrs more) and previous owners have replaced that Yanmar elbow at least twice at over $400-each.