The new owner of the Isalnder took possession on Friday morning and immediately started having issues with the Yanmar 2GM. I feel badly for the guy and told him I would make it right, so far the first mechanic is at a loss, the second mechanic is supposed to look it over today. The symptoms are that it became hard to start, lacks power and smokes sooty black smoke badly all within the last week. The oil and filter was changed in the fall, the fuel filter was not and probably has less than 30 hours run time. When we put it up last fall it ran great, started with no problem and had plenty of power. At the end of the season I topped up the tank with off-road diesel, added an appropriate amount of Cetane booster and used a diesel additive I have never used before from Starbrite. In the past I have always used SeaFoam in the fuel to store for the winter. When troubleshooting such things I always start with what I touched in between when it was fine to when it was not fine....identify the variable I guess. In this case, my big Fall project was to remove the deteriorating engine room foam sound proofing. It was a black crumbly mess. I scraped it all off and replaced it, but got black yick all over the motor. I used a shop vac to remove the stuff, but unknowingly tripped both compression releases. After trying to start the motor to finish winterizing (running antifreeze through it) and having it not start, I read through the Yanmar manual and discovered the releases were in the wrong position. I flipped them and it started right up. Fast forward to Spring launch. The boat went in the water and I did notice it started hard, but then it had been sitting for 8 months so I expected that. I motored over to the slip, tied up and prepped the boat. We never took it out again as we put it up for sale. The broker started it several more times for prospective buyers with no issues. On Friday the broker and new owner motored out of our club over to a nearby marina and could not get more than 3 1/2 knots leaving huge clouds of black smoke. They said the air filter was very dirty, although it was only 2 seasons old I suspect it was full of the engine room insulation. It almost sounds to me like it is running on just one cylinder and the other is not burning the fuel? The first mechanic thinks it may be water in the fuel that ruined the fuel injectors. This Yanmar has only a small single Yanmar fuel filter, no Racor water/fuel seperator.

Any thoughts?