Helps to know which Yanmar. Sorry but I dont follow all the lore on the site close enough to know which Yanmar you have?
In general A failing injector can cause smoke at a cold start but so can several other things. Does the smoke smell like oil burn or is is a putrid half burned diesel smell?
If you have an L series air cooled engine both the pump and injector need to be in tip top condition for them to start easily, run correctly and not smoke especially at start up. Good thing is the Chinese copies have excellent fuel system parts and they are dirt cheap and drop right in.