Reply To: Smoke with Yanmar 4JH2 DTE Engine

[victor crowhurst]

It could be head gasket leaking, it would get worse when the engine is at normal temp under slight load when water is at highest pressure in the cooling system and fuel/air mix is just becoming rich. Check the compressions in each cylinder, wet and dry and also if you can check how long the pressure stays when the piston is at TDC for each cylinder. This may tell which part of the gasket is leaking. It could also be incorrect shotting in the fuel pump, difficult to diagnose and fix, needs a pump engineer with the correct bench test machines- could be expensive.