So, a bit of digging and I have found the issue with the new welder...
Lowest setting is 50amps, not ideal at all for welding bodywork.
The old Mig has a lowest setting of 25amps so no wonder I didnt get these problems before. Now then, I see a way round this if I can find a way of repairing the old welder....
Sorry Burwood, this has hijacked your post so I will take this into a new one.