Universal M25 losing power

I posted earlier this season about the low in oil pressure, and a subtle loss in power on my Universal M25. Briefly; after running for an hour or so, the oil pressure would drop to < 10 PSI on the dash mounted gauge. I also noticed that at WOT that she would rev to 2600 RPM, and not 3K. I believed that I addressed the problem with a quick oil & filter change, as well as changing both the primary and secondary fuel filters.

Since then, I have added 10 gallons of fresh fuel, yet noticed that I am still not achieving the full 3K RPM at WOT.

I was on the boat last night, and had the chance to take a close look while she was secured in the slip. After warming up the engine in reverse, I pressed the throttle to the stop, while still in reverse. I was shocked to see that she would now only reach 2100 RPM at WOT.. I don't normally motor at more than 2K RPM, but this is not good. When she starts (cold) I usually get a puff of white smoke, then it runs clean. There is a little soot on the transom, under the exhaust port, but not much.

I think that I may have to break out the wrenches, and start fixing stuff. The question is, where to begin. One theory is that it could be the mixing elbow blockage. Another is that it may be the injectors are getting fouled.

Under the assumption that it is the injector, I found this;


and this:

And lastly, this which is my exact engine (Kubota D850);

Any other comments, or theories?

Thank you in advance.