Hi, Kristijan & Bob!
Before Steve grabs his pen, a couple of extra questions:
How much oil does the motor consume on 1000 km / 624 miles?
Consumption on gasoline alone?
Consumption on woodgas only? Meaning ONLY!
If the consumption is more on gasoline alone, that’s an indication of some tar buildup has happened on the stems.
If the consumption is less on gasoline, it indicates that the woodgas is wet and
"washes off" the oil-film from the intake stems.
Further more, part-clogging of piston rings by tar increases consumption…
Tar has opposite effect on stem leakage and piston-ring leakage…