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.