White smoke with no diesel smell is the sign of water getting into the engine through a bad head gasket
or cracked head or block, in descending order of ugliness. Is there a sheen of oil in the water around the exhaust? That points to unburned fuel coming of the exhaust.
That the engine wouldn't turn past 1800 (very odd for a Yanmar) and smoked heavily, and now it turns 2200 but produces white smoke suggests fuel problems that could be anywhere from a problem with the high pressure pump
to the injectors. Given how little the engine is used, and given its age, I'm betting that seals
have started to break down and gum up the injectors. Again going back to the age of the engine, I'd just bite the bullet and have the pump
and injectors rebuilt, instead of guessing and groping. With a good mechanic
and a bit of luck, this shouldn't take more than a week to ten days, start to finish.
However, you really, really, really
need to nail down what that white smoke is. I wonder if you aren't looking at two problems: fuel and cooling
. It's not enough to just say "yep, coolant
cap's cool". Have you checked to see if there's any sign of coolant
loss? What does your temperature gauge say? When was the last time you replace the raw water
impeller? How's the belt tension? All of these could be factors in the engine running hot and steaming, not smoking.