What ratio where are you running K ?
Those oil burners like it real rich, but carbon build up is a problem.
R30 oil is the best option, although I have tried Maxima 927 and no complaints from the missus, but costs more than R30 though and can be hard to find.
You could try finding a new missus! I've told mine when she turns 50, I'm going to swap her for two 25 year olds.