did your mechanic set the timing to 15 or 25 degrees yours should be 15 and some mechanics don't know that there is a difference in the models of the 2GM series engines
low compression can be valve setting. make sure that the two end valve rockers are held in towards the center of the engine as they will slip outward during setting with the valve cover off and the valve clearance will be to tight when you reinstall the valve cover.
As you said in your other thread, you had the injectors rebuilt, but haven't clarified what that means. All signals are to a fuel/air problem and injectors are usually at the heart of that. They simply wear out. Other causes could be a blockage or poor fuel pump pressure, but less likely. Although, some get ridiculous with the fuel filters they use and assume that lower microns are always better. Not always true, as your system may clog too fast or overwhelm your pump. Have you checked them? What microns do you use? Also, as I mentioned in your other thread, the rebuilt injectors may have been reinstalled incorrectly, with the wrong seats, so the spray pattern would be affected.
There were 3 different mechanics who worked on the engine over the years. Each time I ask around and try to find someone who really knows what they are doing. The last one (No. 4) I had look at it and took the compression, he works exclusively on diesels. But, he said he works on larger engines and he did not sound that familiar with this engine, he also said the timing is fixed at the factory. The injectors were actually rebuilt 4 seasons ago and again this last season. Unfortunately I don't know what that means since i relied on others. No improvements either time. This is why I have to take matters into my own hands. There are to meny people out there who call themselves mechanicks.
The fuel filters I have always changed myself. There is a water separator mounted up stream of the engine, and the filter on the engine. Even though I don't have the numbers on hand I don't believe that is the problem since I get the same numbers every year to replace them, and the engine used to run better.
I will check the valve adjustments, mixing tube, and I will get a brand new set of injectors and seats, worst case scenario I end up with a spare set. Also, it has been suggested in my other thread to change out all the fuel components.
The Fuel Feed Pomp works fine. Personally, I am leaning towards the Fuel Injection Pump or timing.
I don't know how to trouble shoot the Injection Pump. The Yanmar manual is not very helpful when it comes to trouble shooting.