I have had a similar problem with my Thorneycroft T90 (same engine). It turned out to be a tiny fuel leak in the high pressure fuel pump. Your engine sounds as if it has not had much TLC. It might be a good idea to find your local CAV service place and take the HP pump and injectors there for a...
Re: Old Naval \'Whoop whoop \'horn
Were they not steam powered? I have a vague recollection of when I was in the Navy, getting hold of one to fit to a more modern ship and we had to modify it to work with compressed air.
I have an underwater exhaust outlet and a loop that only just goes above sea level, so have fitted a non return valve (from ASAP) in the exhaust hose just before the outlet. No problems so far.
This is exactly what I had to replace as the baffles that stopped the cooling water flowing back down the dry exhaust had corroded away. I could not find a unit that would fit into the space available so redesigned the exhaust (with the help of an engineer). It now loops up above the waterline...
Yes, the problem is not so much exhaust getting out but water getting in. My exhaust system is a bit low - it does loop above the waterline but not by much and the hull fitting is under water much of the time, so I have put a non return valve just before the hull fitting for peace of mind.