CB750 1980 unburnt fuel

[Motorhead]

These are my compression test results:
#4 170+
#3 165-
#2 165+
#1 170+
So your guess about the valve seals is probably correct.

I am now recording every time I add oil, so in about 4000 km I'll be able to tell, how much it uses exactly between changes.

 

[amc49]

As said most likely elsewhere the seals leak before the rings commonly.