Hi all,

Recently I asked for advice here on my 79 Yanmar 2QM15. Based on advice
here I had the head gasket replaced. A shop inspected the head, but
didn't Xray it, or whatever it is they do. The guy who replaced the head
gasket is apparently at the limit of his abilities, so my next plan is
to have it looked at by a shop. I was hoping I could get some good clues
from the diesel experts here first.

I'm not sure how long the problem I am about to describe has existed but
there may have been versions of the problem present since I bought the
boat a year ago. It has been somewhat intermittent, but seems worse
since the head gasket replacement.

The motor starts hard, but instantly with a squirt of starter fluid. It
runs with a knock at almost all RPMs, but no knock at full throttle with
a little black smoke. After about 5-10 minutes, the power drastically
decreases. It will keep running in neutral, purring like a kitten at all
RPMs, however a fair amount of black fluid pours out of the exhaust, to
float on the water, not much smoke.

Any ideas?

Stephen