The large diameter hole you are looking at, is indeed the air intake. There
should be a semi-circular air induction tube casting attached there. Boats
don't normally have an air filter.
I know of no substitute for the fuel filter, although you could
substitute a completely different assembly I suppose. The filter elements
are still readily availabe.
Your engine was manufactured in 1976 or 1977, but the YSE and YSM
versions, which were manufactured two years previous to, and after the YSB
respectively, are the same engine in most respects.

--
Steve Thomas


"lupi" wrote in message
...
Ahoy, I just bought a small boat with a Yanmar YSB12 diesel in it. It
was owned by hooligans and it seems part of the motor is missing.
There is maybe some kind of hose missing in the front of the engine.
It's directly above the water pump and is an inlet about 2 inches
around. I can see some type of valve inside. This is the air intake?
Is there a picture on line somewhere so I can see what's missing?
Would a generic air filter and housing coupled to a tube work well
enough? Also, is there an inexpensive auto store filter that replaces
CAV 296, a paper filter that goes in the water trap? Also, what kind
of off-the-shelf oil can I use? There doesn't seem to be a lot of info
out there concerning these engines other than that they vibrate
violently at low rpm. I am in the usa. Thanks for your time.