David Cowell wrote:

> After replacing the engine water pump I fired up the Merc 302 and waited for
> the exhaust to show water flow. (using water ear-muff on the I/O) After it was
> obvious there wasn't going to be any, only steam, I shut her down.  Subsequent
> removal of the lower end to look at the pump and passages showed a couple of
> crescent shaped plates with charred rubber.  I assume these used to be part of
> the baffling in the exhausts.  What purpose did they serve and can they be
> replaced without buying the whole exhaust systems?

Those are your exhaust shutters [ flappers ]. It sounds like you have an
old Merc where the flappers are in the lower exhaust pipe, at the T
where the exhaust pipes meet before they leave the back of the boat. Go
to your Merc dealer with your model and serial # , and get all the parts
in that section of the pipe. [ O-ring, flapper, plastic retainer ring ]
In the lower pipe just inside the boat, behind the flywheel housing, you
will see the pipe joint which is held together with three allen bolts.
One set per side. Once inside the exhaust pipe you'll see the recess for
the flapper and the plastic retainer. Insert the flapper, pointing away
from the engine, towards the T. Insert the plastic retainer and o-ring
and reassemble. Good luck.... BTW, the parts list at the dealer shows
the order of assembly. Also a service manual is still available.