Re: Yanmar 2gm20f
Engines running at wide open with no throttle can be oil foaming and what is known as a run away engine, but they produce large volumes of blue smoke.
I had that happen to me the first time I changed the oil in my 2gm20f (put too much in).
Actually, if you had that cloud on the first start, that may have been why, and then something broke while it was "running away".
Now you may have two problems, unrelated except for time.
First, you have a throttle problem. If while it was running away you were frantically jerking and pulling trying to shut it off it may have warped and or broken.
The throttle on a diesel is a complicated mess of stuff with governor springs, weights and fuel rack movement, injection limiters and such. You'll have to consult your manual, wiggle and pull on parts and see what is not moving that should move (or moving that shouldn't).
Second you have a blocked #1 port on your HP pump.
You can take your pump off and take it to a diesel shop to have them look at it. The bad news is that's expensive, the worse news is it's not something you can do yourself (true on most HP pumps).
Frankly, I'd recommend it's time to throw some dollars on it and have a qualified mechanic pick them off. This isn't a old lawn mower.
Lessons learned are opportunities earned.