Welcome aboard from Scandinavia !!!
Had the exact same problem with mine shortly after it arrived here, and it turned out to be the exhaust valve, that was kept slightly open by a tiny piece of whatever.
No appearent indication of it visually, but still more than enough to loose compression and kill any vacuum sucking in fuel.
I simply exercised the exhaust valve with a finger, while spraying the valvestem generously with WD40. In my case this "washed" the contamination away from the valve seat, and compression was regained.