Sorry for the long post, but I hope to help the next person, and to dispel some of the air of "mystery" about diesels, and in particular the M25. Because I have motored more this year than last, I noticed another "issue" with the engine, which, while not related, led me to solve the problem. Please realize that this is only my second season with the boat, and the second year with a diesel...
I bought this boat in the fall of 2010 despite the fact that it had the old-style alternator mounting bracket, and the unpainted aluminum cover led me to surmise that the cover had been cracked by the old bracket. One of the first things that I did was to replace the alternator mounting bracket, and the alternator (upped from 55A to 90A). Here is a pic of the engine when I first saw the boat in June of 2010;
There are at least 7 things wrong in this picture.... Can you find them all?
This year I noticed that there seemed to be a lot of oil leaking out and covering the front of the engine. Last year I replaced the crankshaft oil seal (which was toast), and I assumed that I had done it correctly, and therefore that wasn't the source. Also, the oil seemed to be running down from near the speed control plate on the top of the M25 engine. I looked carefully, and could see no gasket. When I looked in my parts diagram (at home) of the Kubota DH850 Engine, I could see that there should have been a gasket.
Here is a pic of the engine taken much earlier this year, after I replaced the motor mounts;
And this is where I believed the oil was comming from;
Simple, I thought... just buy and install part number 130 in the below illustration.
Here is the CORRECT diagram;
Note that I did not have this on the boat at the time.
A few days later, armed with the new gasket, I tried to install it. Off comes the speed control plate, and I notice that there is a single spring
connected to the speed control lever. The other end of this spring is lost somewhere in the bowels of the fuel injection pump / governor, and I know enough about mucking with governors, to know that I don't want to go there. So I try to slip the gasket over the entire assembly. No joy. The gasket will not slip over without tearing, and I am trying to stop a leak, not start one.
I therefore VERY carefully disconnected the spring, and kept it under slight tension with a loop of wire, and started to install the gasket over the loop of wire. The loop of wire, however, allowed the spring to twist slightly, and the spring disconnected from whatever the other end was hooked on, and it popped out of the engine.
I marked this unexpected turn of events with several special words, reserved for those times when a 15 minute job, suddenly turns out to be a job that may never end, unless you to call for paid help to rescue you.
I then notice ANOTHER spring is lodged down there. Funny, I didn't remember seeing that spring, or know from where it came. so I look in ALL the Universal manuals at my disposal. I can't find it, and the guts of the governor do not look like what I am seeing in any of the illustrations that I have in the service or workshop manuals. Here is one example;
My thoughts at the time; "I am so screwed..."
Well, there is no turning back now, so I plunged ahead. My first thought was to remove the injector pump itself. To get at it, the air cleaner, the intake manifold, and the injector lines have to come off, so off they come. About an hour later, I have the nuts and bolts removed, but this thing won't budge with out breaking something. I try another tack. I have no idea whet lies behind the engine stop lever, but it's got to be easier than the Injector pump. I am trying to be careful here, and I only want one project going at a time. So, I wipe clean all the stuff that I have just removed with a paper towel, and put it back together. I then remove the throttle linkage mounting plate so that I can access all the bolts that hold the stop lever plate in place. Off come the bolts, and after a tap, off comes the stop lever. Here is what I saw;
You can see the small spring exiting off to the right, yet attached to the slot on the fork in the pic above. Once again, no gasket
I noticed that the spring in my hand was far larger than the spring that was sitting, disconnected, in the governor, and reasoned that the larger spring must go over the smaller spring. That is, the smaller spring must be contained within the larger. I also noticed that the end of the spring was bent so that it could slide back and forth about the length of the slot that you see pictured above. If this was true, they must attach to the same mounting points. I reasoned that the smaller spring must be the primary throttle advance, and the larger, would work in conjunction with the smaller as the secondary (heavy load) throttle advance.
Hmmm... and I am having trouble reaching full RPMs.... These two symptoms could be related - yes?
I connected one end of the large and the small spring to the slot seen in the picture above, and then connected BOTH springs to the throttle control lever, and buttoned everything back together... (I still need to buy and install a gasket for the engine stop lever plate.) I bled the fuel system, crossed my fingers, held the glow plug button in, and then hit the starter.
She started right up, and was now idling at about 1400 RPM. After letting it warm up for a few minutes I increased the throttle, and she revved to over 3500 RPM!
I realized that the idle and high speed throttle stops must have been adjusted without the second spring attached, and therefore needed readjusting. I also figured out that the mysterious screw that is buried under a cap, and two lock nuts must be the governor adjustment.
After about 15 minutes of tweaking, I was able to set the idle at 1000, WOT at 3000 RPM, and under load (tied to the dock, in reverse - and I am very confident in my lines and cleats) she will hit 2600 RPM in reverse with a dirty prop. I also know HOW to adjust the governor, should I need to do so.
(that governor adjustment is not labelled ANYWHERE that I could find)