Calling all Engine Experts....
Ok, looking for an engine differential diagnosis.
1985 Yanmar 2GM20F
Motoring out into channel, kick it up to 2400 RPMs at my usual spot, throttle goes all way forward, RPMs decreasing instead, oops, swing boat around with lots of traffic, yell at wife and sister-in-law to break out dock lines (sister-in-law can't tie a cleat hitch), barely make dead stick landing at end of closest finger pier before engine dies. Make visual inspection, no water or diesel leakage, try and start engine again, starts, then dies about 5 seconds, no smoke, but notice what looks like a carbon or exhaust sheen slowly coming from raw water exhaust. Call BoatUS, use unlimited towing back to slip.
Tow boat guy, old salt, says it's definitely a fuel problem.
Wait 2 weeks, then go and change both fuel filters, notice beautiful diesel and no sludge in either primary or secondary. Use bleed screw on secondary with hand pump, get good flow and pump until no bubbles. Do not bleed anywhere else, for example, at the fuel injectors or high pressure line. But I have only bled at secondary filter with hand pump and have never had any issues with air in lines. Try and crank engine, it cranks, then immediately dies, again, with a little of that carbon sheen coming out the exhaust at the transom. I put my finger in it, definitely not oil, like exhaust carbon in water.
Other things, maybe related or not.
Mixing elbow extremely rusted on outside. When I bought boat 5 years ago, mechanic who did work on engine said that elbow worried him, he would change it given how rusted it was on outside. Also, I have very poor access to the back of my engine, but leaned in and noticed that hoses leading to mixing elbow are also deteriorating.
Fuel: I usually keep tank at 3/4 to full and use biocide. This year I let tank get to 1/2 and have had some bumpy rides, but again, no sludge in filters.
Black spray: I have noticed back in my engine housing, under and around the mixing elbow, a small amount of black spray on the bilge paint.
Fresh water hose: while doing an examination, I noticed that the fresh water line was resting on top of the engine block and gradually making a hole in the rubber. I don't have any fresh water or coolant leakage yet and not overheating or loss of coolant, but I will have to re-route or secure regardless.
So what do you all think?
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