Stalling

I have a Yanmar 3HM, 3 cylinder, 27 hp. The engine runs fine, starts easily. The problem is that it stalls when the throttle is pulled back to idle rapidly, as when docking. If I ease the throttle back slowly it keeps running. After it stalls I can restart it immediately. The idle is set correctly at least as far as I can rely on my new tachometer. I have been through the fuel supply from the tank to the mechanical fuel pump, new hose, filter etc etc looking for air suction leaks. I have a section of clear tubing coming that I will put between the filter and pump to look for air bubbles, should have it in a couple days. I have also heard of putting the clear tubing in the return line?

The engine is new to me I have only a couple hours running time. I have heard that the three cylinder engines can vibrate at some engine speeds and this one certainly does that. At 1500 it has very noticeable vibration but smooths out at around 2000. I have done nothing with injectors.

maybe try bumping up idle a bit, might be a crutch but better than being dead in the water while docking

Don't know the engine, but every diesel I've seen use a governor or a governor in the injector pump to control the engine speed. If the engine falls below idle and dies, the governor is at fault. It may be gummed up to a small degree. Probably from sitting or light use over time. Using a fuel additive that removes deposits might solve the problem. Better biocides usually have this in the mix. Try a triple dose.
Could be some of the vibration, too.

Typical problem of Dirty injectors