Hi folks; just bought a little runabout and thought someone might know what to do-I know its not an Omega but there are many clever fixers on here

It is a 989cc Daihatsu engine, 3 cylinder 12v, double overhead cam, which was stinking of oil when it arrived. Traced this to a split oil filter seal, did an oil and filter change and cleaned the mess off, now dry.
I have had three cars with the same engine, but this one is just not quite right:
Happy when cold, lazier when warm
Happiest on light throttle, bogs slightly on full throttle
Using a little oil
Black smoke on full throttle when standing
Very fumy, mildly eggy under demand
Slight smoke from hole where dip goes in, when hot and dipstick removed
I have checked the plugs, changed the oil, used posh fuel and treatment and then thrashed it to undo 27k of OAP pootling, checked underside on ramp and exhaust is nearly new and leak free, air filter changed and box hoovered. No oil in water, water in oil.
These engines are usually bomb-proof and do 150k without issue. Ideas, anyone?
Much appreciated (especially as not Omega!)
