niekie ,
your are right i did not think it should have an effect on the arc , so i changed wires (back to308l) and the arc seemed better again.Needless to say it is still puzzling?!
I tried different gas mixtures a(98/2,tri-gon),which did help with the residue but not with the arc.
Does the addition of si help remove contaminants inthe base metal as in 70s6 for carbon?
thanks for your help,
mike wright